The attack struck Madina mosque in the Unguwar Shuwa area of Mubi, around 200km (125 miles) from the Adamawa state capital, Yola.
"As I am talking to you, I saw over 22 dead with many injured including the suicide bomber, " said a resident who simply identified himself as Bello.
Security analysts said it again underlined the threat posed by the Islamic State group affiliate, despite an overall decline in deaths from attacks by the group past year.
A National Emergency Management Agency (NEMA) staff inspects the damage at the site of a suicide bomber attack in Mubi in Adamawa state, in northeastern Nigeria November 21, 2017.
Reports say that the 17-year-old bomber entered the mosque along with other worshippers and triggered the blast immediately after the prayers. "We don't suspect anyone specifically but we know those behind such kind of attacks". However, a reporter on the scene said the death toll was no more than 27, all men and boys.
"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.
In a statement, the president's office said the government would do "everything required to secure the state from the deadly menace of Boko Haram".More news: Uber orders huge fleet of autonomous Volvos
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A civilian militia source embedded with the military told AFP the attack was likely to have been to "shore up morale" after a series of recent losses in the remote region.
Boko Haram held territory in Adamawa state in 2014.
"They are feeling the heat".
Adamawa, the state where Mubi is located, is no stranger to Boko Haram's violent attentions, according to NPR's Ofeibea Quist-Arcton.
The town's name was changed temporarily to Madinatul Islam, or "City of Islam" in Arabic, during the Boko Haram occupation. The extremists' offensive has also spilled over into neighboring Chad, Niger and Cameroon.
He said, "Today's attack appears to be yet another example of Boko Haram's continued unlawful disregard for human life".