The attack on a market in the city of Potiskum, the commercial capital of Yobe state, was the latest in a string of suicide strikes in which children have been used.
The initial death toll given by witnesses and hospital sources was six, the bomber and five others but medical sources at the state-run hospital in Potiskum said later two of those injured had also died.
Nineteen people injured in the blast were taken to the hospital, a local vigilante leader, Buba Lawan, told AFP.
The bombing highlights the severe security challenges facing Nigeria in the run-up to presidential and parliamentary elections on March 28.
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During a swing through neighbouring Chad, Cameroon and Niger, French Foreign Minister Laurent Fabius yesterday urged Nigeria to entirely commit itself to battling Boko Haram.
"It is necessary that there be full commitment from Nigeria in the fight against Boko Haram," Fabius told reporters in Niger's capital, Niamey.
On Saturday in the Chadian capital N'Djamena, Fabius visited a coordination cell set up on a French military base to liaise between Cameroon, Chad, Niger and France.
President Goodluck Jonathan, who has been in office since 2011, is engaged in a tough re-election campaign against ex-military ruler Muhammadu Buhari.
Voting initially scheduled for February 14 has been delayed for six weeks to give Nigeria's military time to secure the country, despite its failure to beat back Boko Haram in the previous six years.
Jonathan admitted in an interview published yesterday that early on in their rise he had underestimated the Islamists, who have overrun swathes of the northeast.