The improvised explosive device was triggered by remote control at a parking area set up a kilometre away from the venue of the public meeting at Charsadda in Khyber-Pakhtunkhwa province. A woman was among the injured, officials said.
The ANP chief had not arrived at the venue when the bomb went off. Police cordoned off the area and launched a search operation. The ANP said it would go ahead with the meeting.
No group claimed responsibility for the blast though such attacks are usually blamed on the Pakistani Taliban.
Dozens of ANP leaders and workers have been killed by the Taliban over the past five years.