The 7.1-magnitude earthquake hit on Thursday near the epicenter of last month's 9.0-magnitude quake.
The aftershock did not cause a tsunami and it appears that the area's nuclear plants did not suffer any more damage.
Two people were killed, national fire and disaster agency spokesman Junichi Sawada said Friday. A 79-year-old man died of shock and a woman in her 60s was killed when power was cut to her oxygen tank. More than 130 people were injured.
The 7.1 quake knocked power to much of the area. Nearly a million homes suffered blackouts in Japan's northeast.
The new tremor threw even more areas into disarray and sent communities that had made some gains back to square one.
Gasoline was scarce again, and long lines formed at stations. Stores that had only recently restocked their shelves sold out of basics Friday and were forced to ration purchases again.
Meantime, the search continues for the victims of last month's tsunami. More than 15,000 people are still missing from that disaster.
The Associated Press contributed to this report.
