The attack took place late last night in the Mekhtar area of Loralai district.
A senior police official said a dozen militants had come on motorcycles and opened indiscriminate firing on the check post.
"It was a deadly attack and five including three constables were killed on the spot," SSP Imran Shaukat said.
The check post was also damaged and a police mobile was destroyed during the attack.
The situation turned tense in the area following the attack.
Tehrik-e-Taliban Pakistan claimed responsibility for the attack.