Ten other policemen were injured in the attack, provincial governor spokesman Omar Zwak said, according to the TOLO broadcaster.
The attack took place in Helmand's district of Nawa on Friday night, the news outlet added.
The number of casualties among the police servicemen could be higher, as some sources claimed that at least 10 policemen were killed as a result of the attack, the broadcaster added.
Afghanistan has long been suffering from unstable political, social and security situation due to the activity of Daesh (banned in Russia) and the Taliban. The Afghan National Defense and Security Forces are currently conducting joint offensive operations to combat terrorism across the country.