Police say the young bomber was mingling with worshippers in the town of Mubi when he detonated his explosives - an act described by President Muhammadu Buhari as a "very cruel and dastardly suicide bombing attack".
He tweeted: "My condolences to the families of the victims, and the government and people of Adamawa State. May the souls of the dead rest in peace."
Police spokesman Abubakar Othman said the number of dead could rise further "as those seriously injured could add to the figure", adding that they were "still trying to ascertain the number of injured because they are in various hospitals".
The explosion bore the hallmarks of a Boko Haram attack. The extremists - based in neighbouring Borno state - often strike with suicide bombings in crowded public places like mosques and markets.
Abubakar Sule, who lives near the mosque, said he was present during the rescue operation and that 40 people died on the spot while several others were taken to hospital with severe and life-threatening injuries.
He said: "The roof was blown off. People near the mosque said the prayer was mid-way when the bomber, who was obviously in the congregation, detonated his explosives.
"This is obviously the work of Boko Haram."
Yan St-Pierre, a counter-terrorism specialist at the Modern Security Consulting Group in Berlin, said the bombing fitted a pattern of previous attacks.
"It fits with the increasing lethality and potency of suicide attacks of the organisation's current 'hot streak', which started approximately four weeks ago," he said.
Mubi is in Adamawa state, where Boko Haram held territory until the Islamist militants were pushed back by troops in early 2015.
The latest attack is the highest loss of life since 56 people were killed in the same state last December, when two schoolgirl suicide bombers killed 56 people and wounded dozens more in a crowded market.
Boko Haram has waged an insurgency in northeast Nigeria since 2009 - killing more than 20,000 and forcing more than 2.4 million people in the Lake Chad region to flee their homes in an attempt to create an Islamic State.
Most attacks by the group focus on Borno state, the birthplace of the insurgency.
The group held a swathe of land around the size of Belgium in Borno, Adamawa and Yobe states until early 2015 but were forced out by Nigeria's army backed by troops from neighbouring countries.