Japan's Meteorological Agency says the quake struck early Saturday 10 kilometers (6 miles) below the sea surface off the coast of Fukushima, northeast of Tokyo.
The agency issued tsunami advisory along the Japanese northern coast.
Public broadcaster NHK says the Fukushima Dai-ichi nuclear power plant is checking if there is any damage from the quake.
The 2011 disaster killed about 19,000 people. That disaster also triggered multiple meltdowns at the Fukushima plant. More than 100,000 people are still unable to go home due to fear of radiation contamination from the plant.