The focus was initially detected at 37.1 degree of north latitude and 140.7 east longtitude, with a depth of 20 km. The epicenter was close to the crippled Fukushima Daiichi nuclear plant.
The quake was registered at upper 5 in Japan's seismic intensity scale of 7 in parts of the prefecture.
No tsunami warnings were issued and no immediate reports on damage and injuries.