Governor’s spokesman Omar Zwak said the explosive-laden motorcycle was detonated at about 7.30pm.
He said the explosion took place in front of a shop and all victims are civilians.
Zwak also stated that there were no military installations or checkpoints near the blast site.
No group has claimed responsibility for the explosion.
Another tragedy meanwhile unfolded in the same province earlier in the day when eight people drowned in the Helmand River after their boat capsized.
According to Zwak, the incident happened on the river in the Kajaki district.
He said there had been three men, three women and two children on the boat at the time of the incident.
Kajaki Dam gates were closed during the day as people searched for the bodies.