An improvised explosive device was planted roadside along Nala Tochi and it exploded when vehicle of Malik Saeed, a local tribal leader, went past it.
The attack happened in the town of Bakakhel 150 kilometres (93 miles) south of Peshawar.
Malik Sayed Ali Wazir, who headed an anti-Taliban militia in the town, died on the way to hospital while his son was fighting for his life.
No group has yet claimed responsibility for the killing but attacks on pro-government tribal elders by militants across northwest Pakistan are not uncommon.
Bannu also borders the lawless North Waziristan tribal district. Pakistani troops in June last year began a long-awaited drive to clear insurgent bases in the district after a bloody attack by the Pakistani Taliban on Karachi airport sank faltering peace hopes.
The army has intensified its offensive since the Taliban’s massacre of 153 people, 134 of them children, in a school in Peshawar last December.