A 38-year-old woman has been charged with aggravated robbery after allegedly stealing a car at knifepoint in Canberra on Thursday.

The woman was expected to appear in the ACT Magistrates Court on Saturday morning. She also faces a charge of drive motor vehicle without consent.

In a statement on Saturday morning, ACT Policing said a member of the public reported seeing the allegedly stolen Mitsubishi Mirage parked on Corrina Street in Phillip.

Officers allegedly found the 38-year-old in the driver's seat.

The woman's arrest came after police had appealed for witnesses to the alleged aggravated robbery and sightings of the vehicle.

Police allege that the 20-year-old Mirage owner was sitting in the vehicle on Denigan Street in Erindale about 9pm on Thursday when a woman approached her and threatened her with a large kitchen knife, demanding the alleged victim's phone and the vehicle.

Police say the 20-year-old ran to a nearby service station and the alleged offender drove away in the vehicle.

More to come.