Police said a man forced out of her vehicle at a car park on Bankmore Street in Belfast city centre at about 18:25 BST on Monday.
The suspect got into the woman's car but was preventing from driving off when other people came to her aid.
Police have arrested a 20-year-old man on suspicion of hijacking.
He is also being questioned on suspicion of criminal damage and possessing an article with blade or point in a public place.
A PSNI spokesman said the woman was not injured but was "left shaken by her ordeal".
A woman who was threatened with a needle during a hijacking has managed to stop a man from taking her car, with help from members of the public.