The Mendocino County Sheriff's Office reported that the incident occurred at Savings Bank of Mendocino County on Highway 101 in Hopland shortly before 3 p.m.
Authorities were alerted by a 911 call reporting the bank robbery.
When deputies arrived witnesses told them that the suspect – a white male adult – had fled in a vehicle, which witnesses described, according to the sheriff's report.
Deputies and Ukiah Police, along with the California Highway Patrol, searched the area for the vehicle, with CHP stopping a vehicle that matched the description at about 3:30 p.m.
Officials said the vehicle's single male occupant was detained and witnesses identified him as the person who allegedly robbed the bank. Evidence found in the car is alleged to have confirmed his involvement in the robbery.
The suspect, who was arrested at the scene, was not identified by officials on Wednesday.
Sheriff's officials said an investigation into the suspect's possible involvement in other robberies currently is under way.