It's the second strong quake to rattle the country in a 24-hour period.
There have been no reports of damage or tsunami warnings issued because of either quake.
The latest temblor struck south of the main northern island of Hokkaido at about 7:30 p.m. PT.
A magnitude 6.1 quake struck off the coast of the Fukushima nuclear power plant early Thursday morning, the same area that was ravaged by an earthquake and tsunami in March.
