The pastor of the church, a woman and her two children, both boys, were among the deaad.
Two other worshippers and the suicide bomber also lost their lives
The explosion occurred at about 9:30am on Sunday.
“People were just going to the church when the bomber entered, otherwise the casualty figure would have been higher,” said Red Cross official Hassan Alhaji Muhammad, who visited the scene of the blast on the outskirts of Potiskum.
He said the bomber mixed with members of the congregation as they were entering the church.
A hospital in Potiskum said it had received the bodies.
Suspected Islamist militant gunmen and bombers killed more than 200 people last week in a spate of bloodletting that prompted renewed outrage and calls for an international meeting to coordinate the offensive against Boko Haram.
Buhari is due to visit his counterpart in Cameroon after the Muslim holy month of Ramadan and meets U.S. President Barack Obama on July 20, when the fight against Boko Haram is likely to be high on the agenda.
Presidential Spokesman Femi Adesina said Saturday Buhari would keep his pledge to defeat the Islamists but added that the government did not rule out talks with the insurgents.
“If Boko Haram opts for negotiation, the government will not be averse to it,” Adesina said a statement.
“Government will, however, not be negotiating from a position of weakness, but that of strength.
“President Muhammadu Buhari is resolute. He has battled and won insurgency before, he is poised to win again,” he added.
More than 650 people have been killed in separate terror attacks since President Muhammadu Buhari was sworn in on May 29.