The governor's stitches were clearly visible after the accident
Arnold Schwarzenegger did not have the proper licence to drive a motorcycle when he crashed at the weekend, Los Angeles police have said.
The California governor and former action movie star required 15 stitches to his lip after being injured in the traffic accident in Los Angeles.
Questioned by reporters, he admitted he had never applied for the right licence after moving to the US in 1968.
"It was just one of those things that I never really did," the governor said.
The admission may mean he has been breaking the law for years.
Los Angeles police say they have forwarded the case to the city attorney's office for possible prosecution.
The governor could face a fine.
Mr Schwarzenegger is well known as a Harley Davidson fan who rides California's Pacific coast highway with friends.
He was riding a motorcycle with his son at the weekend when a car reversed in front of him, his spokeswoman said.
Patrick Schwarzenegger, 12, who was riding in the motorcycle's sidecar, was treated at hospital for cuts and bruises, she said.
An Austrian-born former bodybuilder and Hollywood movie star, Mr Schwarzenegger was elected governor of California in 2003 and has confirmed he will seek re-election next year.
He spent four days in hospital in 2001 after breaking six ribs when his motorcycle collided with a car in front of him.