Judge Thokozile Masipa said the athlete was guilty of negligently handling a firearm in a restaurant, but acquitted him of firing a gun from his car.
The judge on Thursday cleared him of murdering Reeva Steenkamp last year.
She said the state had failed to prove he intended to kill the model.
Mr Pistorius admits firing through a toilet door at his home but says he mistook Ms Steenkamp for an intruder.
He could still be convicted of culpable homicide over her death.
The athlete had arrived at court surround by bodyguards on Friday morning, pushing his way through a scrum of journalists to get inside the, where Ms Steenkamp's family were already assembled.
The day before, prompting tears from the Olympic and Paralympic sprinter, Judge Masipa said he could not have foreseen killing whoever was behind the toilet door - but went on to say that he had acted hastily and with excessive force.
She described his actions as negligent.
BBC correspondents said the judge appeared to be leaning towards the lesser charge of manslaughter, known in South Africa as culpable homicide, when she adjourned unexpectedly for the day.
The charge of culpable homicide implies negligence without intention to kill and could still mean a jail sentence of up to 15 years. Legal experts suggest seven to 10 years is more likely.
The double amputee had denied murdering Ms Steenkamp after a row on Valentine's Day last year, saying he shot her by mistake.
Mr Pistorius, 27, has pleaded not guilty to all the charges he faces, including two counts of shooting a firearm in public and the illegal possession of ammunition.
Analysis: Pumza Fihlani, BBC News, Pretoria High Court
While finding Oscar Pistorius not guilty of murder, Judge Masipa appears to be leaning towards the lesser charge of manslaughter, known in South Africa as culpable homicide.
Minutes after the lunch break, she seemed to be on the verge of announcing her verdict, only to stop abruptly and adjourn until Friday - leading to sighs and gasps in the overflow court.
Following a long trial that has gripped people around the world, Judge Masipa seems to want to give a detailed account before announcing her verdict. South Africa's legal system has also been on trial and many believe the athlete is getting off lightly, possibly because of his fame.
But legal experts argue that the judge has merely followed the law and the evidence before her. The onus was on the state to prove its case beyond reasonable doubt, which the judge said it had failed to do.
Verdict unsettles legal experts
How judgement was tweeted
Most of the trial, which began on 3 March 2014, has been televised and attracted worldwide attention.
Before the fatal shooting, Oscar Pistorius was feted in South Africa and known as the "blade runner".
He had won gold at the London 2012 Paralympic Games and also competed at the Olympics.
Ms Steenkamp, a 29-year-old model and law graduate, was hit three times by bullets shot through the toilet door by Mr Pistorius at his home in the capital, Pretoria, in the early hours of 14 February 2013.
He denied the prosecution's allegation that the couple - who had been dating for three months - had rowed. The judge also said she had not been convinced by the efforts to prove that the couple had rowed.
The athlete said he thought his girlfriend was still in the bedroom when he heard a noise in the bathroom, which he believed to be an intruder.
In July, a psychiatric report requested by the judge said Mr Pistorius had post-traumatic stress disorder but no mental illness that could prevent him being held criminally responsible for his actions.
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Mr Pistorius said in his statement at the start of the trial that he woke in the early hours and  walked on his stumps to the balcony, pulled in two fans, closed the sliding door and drew curtains. He said that shortly before he had spoken to Reeva, who was in bed beside him.
He said he rejected prosecution claims that a witness heard arguing coming from the house before the shooting.
Mr Pistorius said he heard the bathroom window sliding open and believed that an intruder, or intruders, had entered the bathroom through a window which was not fitted with burglar bars.
"Unbeknown to me, Reeva must have gone to the toilet in the bathroom at the time I brought in the fans," he said.
Mr Pistorius said he approached the bathroom armed with his firearm, to defend himself and his girlfriend, believing Ms Steenkamp was still in bed.
Both sides agree four bullets were fired. Ms Steenkamp was hit three times.
Mr Pistorius said he fired his weapon after hearing a noise in the toilet which he thought was the intruder coming out of the toilet to attack him and Ms Steenkamp.
He said he was in a fearful state, knowing he was on his stumps and unable to run away or properly defend himself.
Mr Pistorius said he rejected claims that he was on his prostheses when he shot at the door.
A witness told the trial she woke to hear a woman screaming and a man shouting for help. She said that after the screams she heard four shots.
Mr Pistorius said he went back to the bedroom after shooting at the toilet door, still shouting for Reeva. Lifting himself up onto the bed, he felt over to the right hand side of it and noticed Ms Steenkamp was not there.
Mr Pistorius said this was when he realised she could have been in the toilet.
Mr Pistorius said he went back to the bathroom but the toilet was locked, so he returned to the bedroom, pulled on his prosthetic legs, turned on the lights before bashing in the toilet door with a cricket bat.
Forensics expert Johannes Vermeulen told the court that the height of the marks on the door caused by the cricket bat suggest Mr Pistorius was on his stumps at the time.
Mr Pistorius's defence team say he then called security at the gated housing complex and a private paramedic service before carrying Ms Steenkamp downstairs.
A security guard claimed it was the other way round, and he had called Mr Pistorius first after reports of gunfire. However, phone records shown to the court revealed Mr Pistorius called the estate manager at 3:19am, a minute later he called the ambulance service and at 3:21am he called estate security.
A minute later he received an incoming call - estate security calling him back.
According to police phone expert Francois Moller, Mr Pistorius called his friend Justin Divaris a short time later and just after 4:00am he called his brother Carl.
The judge in the Oscar Pistorius murder trial has found the athlete guilty on a firearms charge, but is still to rule on whether the athlete is guilty of the culpable homicide of his girlfriend.