It was being attended by many anti-Taliban militiamen in the region. At least 40 people were wounded.
Several anti-Taliban tribal groups are based in the area and they are often targeted by the insurgents.
A spokesman for the Taliban told the BBC that they had carried out the bombing.
He said it was in retaliation for the support by local tribal militia of the continuing anti-Taliban operation by Pakistan’s security forces.
An injured man is taken into the hospital in Peshawar It is the second major bombing in as many days in Pakistan
Survivors of Wednesday’s bombing complained there was no police protection although the militiamen are targeted regularly.
The bomber targeted the funeral of the wife of Hakim Khan – a leader of the anti-Taliban tribal force in Adezai, some 15km (10 miles) from Peshawar city.
Mr Khan was instrumental in raising the force, known as a lashkar, with the support of the government to fight militants.
Correspondents say that it was not immediately clear if Mr Khan was killed or wounded in the explosion.
The procession was on its way to the cemetery when the attack took place.
“As we are readying for prayers, a boy wrapped in a shawl headed towards us. People shouted to the imam (prayer leader) to wait for him to join us but as he came close he blew himself up,” witness Mehmood Shah told the Reuters news agency.
The ground was strewn with the dead and wounded. Hats were scattered around and there was a pile of shoes left behind the victims.
Rescue workers were quick to reach the scene and the injured were taken to hospitals in Peshawar, where a medical emergency was declared.
The BBC’s Syed Shoaib Hasan in Pakistan says the militants aim to discourage local citizens from helping the security forces.
Adezai, located in the Mattani area, has been the centre of a tribal anti-Taliban force raised with the government support.
The head of the force, Abdul Malik, was killed in a bomb attack in 2009.
The area has also seen frequent Taliban attacks on police stations and security posts.
Until recently, the tribal anti-Taliban force had been conducting night patrols to discourage Taliban attacks but it ended some weeks ago as the government’s supply of arms and ammunition to the members of the force dwindled.
The attack comes a day after at least 26 people were killed and more than 120 injured in a car bomb explosion at a gas station in the industrial city of Faisalabad.
The Taliban said they were behind Tuesday’s attack. Most markets in the city were shut on Wednesday as residents mourned the dead.
Source: BBC