The bomber struck just after 57-year-old Rehman's motorcade entered Charsadda town in Khyber-Pakhtunkhwa province, where he was to address a gathering at Darul Uloom Islamia seminary.
The powerful blast occurred near a government office and a private school, witnesses said.
Eight persons, including four policemen and a woman, were killed while 29 others, including security personnel and Jamiat Ulema-e-Islam (JUI) workers, were injured, officials said.
Geo News channel quoted police as saying that the attack was carried out by a suicide bomber.
"I am fine. There was a powerful explosion near my car and the windscreen was shattered. Another car in my motorcade was damaged," Rehman told the media.
He said one or two members of his security detail and several policemen deployed in the area were injured by the blast.
Rehman cancelled his meeting in Charsadda after the blast. The seriously injured persons were taken to a hospital in Peshawar. No group claimed responsibility for the attack.
Rehman had escaped a bid on his life yesterday also when a suicide attacker tried to target his motorcade at Swabi in Khyber-Pakhtunkhwa province. That attack killed 10 people, including two policemen.
The attacks have surprised political observers as the JUI is perceived as being pro-Taliban.
Rehman has repeatedly called on the federal government to halt military operations against the militants.
Rehman told the media today that he had not received any threats. He refused to say who could be behind the two attempts on his life.