The powerful explosion was heard from several kilometres away and caused panic in the area.
State-run Radio Pakistan reported that 5 persons were killed and 15 injured by the explosion.
No group claimed for the attack though the banned Tehrik-e-Taliban Pakistan has repeatedly targeted the ANP and other secular-leaning parties like the Pakistan Peoples Party and Muttahida Qaumi Movement during the campaign period.
Several ANP and MQM members, including candidates, were killed in Taliban attacks.
Days before the polls, the Taliban threatened it would carry out attacks, including suicide bombings, on election day.
The threat heightened concerns about security for the polls, which mark the first democratic transition of power in Pakistan's history.