The plane landed on the northbound side of the highway just north of Farm Hill Road in Woodside around 7:15 p.m. Sunday.
For a while, all four lanes of the freeway were blocked, but video sent to ABC7 News about a half-hour later showed traffic was moving again.
It wasn't immediately known why the plane landed on the freeway.
The California Highway Patrol was investigating the incident. There were no injuries reported.