Local government officials said the police officer opened fire at a checkpoint in the Kushki Kohna district of Herat province and was at large after the killings, Khaama Press reported.
One official said the assailant took weapons from the checkpoint with him.
It wasn't immediately known if the gunman had ties with militant groups, the official said.
Officials also told Khaama Press at least 16 Taliban militants were killed and six others wounded during a coordinated military operation conducted by national security forces in several provinces .
Afghan army Gen. Zahir Azimi said soldiers seized 25 improvised explosive devices during the operations.
Taliban militants denied the reports concerning the military operations, calling them baseless.
In another report from Khaama Press, an Afghan national army soldier was killed in a roadside explosion in southern Helmand province.