Mohibullah Mohib, a spokesman for the provincial governor, said two militants were killed in the incident late on July 23.
Mohib did not reveal where in the province the attack took place.
In a statement, the Taliban claimed responsibility for the attack.
The militants have launched near-daily attacks on Afghan security forces, even as peace efforts have been gaining momentum to put an end to Afghanistan's nearly 18-year war.
The Taliban control or contest around half of the country, controlling more territory than any time since the U.S.-led invasion in 2001 ousted the group from power.
The Taliban controls large parts of Farah, which is located on the border with Iran.
Farah has been the scene of fierce fighting between the militants and government troops in recent years.