The attacks took place in the coastal city of Half Moon Bay. Some of the victims were Chinese-American.
Suspect Chunli Zhao, 66, was arrested after driving to a police station.
It comes as the state mourns the deaths of 11 people in Monterey Park - about six hours south-east of Half Moon Bay - during Lunar New Year celebrations.
And just over a week ago, six people including a teenage mother and baby were killed at a property in Goshen, central California.
