The bomber, who was riding a motorcycle, detonated his suicide vest minutes after Rehman's motorcade passed the police post in Swabi area of Khyber-Pakhtunkhwa province, district administration chief Syed Abdul Jabar Shah told reporters.
A police official was among the seven persons killed by the powerful blast, Shah said. Most of the dead and injured were Jamiat Ulema-e-Islam (JUI) supporters who had gathered at the police post to greet Rehman, witnesses said.
Seven of the injured were in a serious condition and could be shifted to Peshawar for treatment, officials said.
A JUI spokesman said Rehman, who had arrived in Swabi to address a public meeting, was safe.
No group claimed responsibility for the blast. The attack 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. JUI sources said the attack was aimed at targeting party chief Rehman.
District police chief Ijaz Khan said a large police contingent had been deployed in the area to provide security to Rehman.
Prime Minister Yousuf Raza Gilani strongly condemned the blast and described it as an "inhuman act of the militants who have no regard for human lives or religion."
Such acts cannot undermine the government's efforts to wipe out extremism and militancy, he said.