Unidentified people flung a hand grenade at a police and FC checkpost in Bara Sheikhan. Police cordoned off the area and also started a search operation.
No group has so far claimed responsibility for the attack.
Militants have often targeted police in attacks in the northwestern regions of the country.
Khyber-Pakhtunkhwa and tribal areas have been struck by violence since hundreds of Taliban and al Qaeda fighters sought refuge there after the US-led invasion of Afghanistan in 2001.
The government has claimed a number of military successes against the hardliners over the past two years, but attacks continue across the country and are concentrated in the northwest.
Pakistan launched its most ambitious military offensive yet against Taliban militants in South Waziristan in 2009.
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