The quake's epicenter was 133.6 miles west-southwest of Eureka, according to the U.S. Geological Survey. Its depth was measured at 3.6 miles shortly before 1 p.m.
There were no immediate reports of injuries or damage to any coastal areas.
Two earthquakes of similar magnitude were initially reported by the USGS, but the agency later clarified that only one temblor had occurred.
The epicenter was located in the Mendocino Fracture Zone, an area of frequent seismic activity.
Tsunami Info Stmt: M5.8 140mi SW Eureka, California 1250PDT Sep 22: Tsunami NOT expected— NWS Tsunami Alerts (@NWS_NTWC) September 22, 2017