The Pakistan Taliban, also known as Tehrik-e-Taliban Pakistan (TTP), claimed responsibility for the attack in a statement.
Police said the bombing took place in Dera Ismail Khan district, where security incidents have been frequent this month, including attacks involving the Pakistani Taliban.
In a related development, the attack came a week after a similar incident in Kohat district, also in Khyber Pakhtunkhwa province and bordering Afghanistan.
In that attack, an assailant rammed an explosives-laden vehicle into a mosque, causing the outer wall of a police office building to collapse and badly damaging the mosque.
The bombing killed 21 people and wounded 78 others, with 15 police officers among those killed because the attack occurred near a building housing police offices.