There were no immediate reports of casualties or property damage. The agency did not issue a tsunami warning.
The epicentre of the 7.54 p.m. (1054 GMT) quake was off Fukushima prefecture, the agency said.
There have been no reports as to whether the stricken Fukushima I nuclear power station was affected by the earthquake.
The same region was hit by a 9.0-magnitude earthquake and resulting tsunami March 11.
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