The quake struck at a depth of 42.3 kilometres in the Pacific Ocean 34 kilometres east-northeast of the town of Namie, the US Geological Survey said.
The Japan Meteorological Agency said there was no risk of a tsunami from the quake, which caused some swaying in high-rise buildings in Tokyo.
There were no immediate reports of damage or injuries though some local service train services stopped, public broadcaster NHK reported.
Tokyo Electric Power, operator of the Fukushima plant, said no abnormalities were detected.
In November a powerful 6.9-magnitude quake sparked panic and triggered a one-metre (three-foot) tsunami that washed ashore at the Fukushima plant but caused no damage.
Japan sits at the junction of four tectonic plates and experiences a number of relatively violent quakes every year.
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