George Hamilton added that some of its members were involved in the murder of ex-IRA man Kevin McGuigan Sr last week.
But he said there is no evidence at this stage that the killing was sanctioned by the organisation.
The police assessment, he said, is that the Provisional IRA remains committed to politics and is not engaged in terrorism.
Mr Hamilton said that "some of the Provisional IRA structure from the 1990s remains broadly in place" but its purpose "has radically changed since this period".
"They are not on a war footing, they are not involved in paramilitary activity in the sense that they were during the period of the conflict," he said.
Mr McGuigan, 53, died after he was shot at his home in east Belfast in what detectives believe was a revenge attack for the killing of former IRA commander Gerard 'Jock' Davison in Belfast in May.
The chief constable said the two murders were the results of a "fall-out" within the republican community.
"Some current Provisional IRA and former members continue to engage in a range of criminal activity and occasional violence in the interest of personal gain or personal agendas," he added.
Mr Hamilton said the PSNI had no information to suggest that "violence as seen in the murder of Kevin McGuigan" was "sanctioned or directed at a senior level" in the republican movement.
The main unionist and nationalist parties met with Mr Hamilton on Saturday to discuss the police probe into killing.
Sinn Féin MLA Gerry Kelly said his party would support the investigation.
And he reiterated remarks by the party's president Gerry Adams in which he said the IRA was not involved in the murder.
"The IRA stood down over 10 years ago," Mr Kelly said.
"Sinn Féin's commitment to peaceful and democratic progress is beyond question."
He added that the party had raised with Mr Hamilton "concerns about a number of speculative and unhelpful comments made recently".
The DUP's Gregory Campbell said his party would be meeting with the Northern Ireland Secretary of State Theresa Villiers about the alleged role of IRA members in the killing.
He added that there was no surprise among his party at the suggestions of IRA involvement.
The Ulster Unionist Party also met with Mr Hamilton on Saturday.
Party leader Mike Nesbitt said afterwards that Sinn Féin's credibility was "in tatters" and it needed to "accept some responsibility" for Mr McGuigan Sr's killing.
"They continue to insult our intelligence by claiming no IRA involvement in this latest murder," Mr Nesbitt said.
After the SDLP's meeting with the chief constable, its leader Alasdair McDonnell said the "skeleton" of the IRA remains in existence.
But he said the evidence was not there to collapse the assembly.
That came in response to comments from First Minister Peter Robinson, who said he would discuss the prospect of excluding Sinn Féin from the executive with other Northern Ireland parties.
The chief constable of the Police Service of Northern Ireland (PSNI) has said the Provisional IRA still exists.