Provincial governor spokesman Omar Zwak said the incident took place at around 12 a.m. when a sticky bomb attached to a vehicle went off.
He said three civilians were injured in the explosion.
However, a local medical official said that one of the victims died on the way to the hospital due to severe injuries.
Immediately, there was no claim of responsibility for the incident.
Helmand is among the volatile provinces in the south of Afghanistan where the Taliban insurgent group is actively operating in a number of its districts and usually carrying out attacks against government forces.