The gunmen ambushed the car near the remote Sher Afzal Banda area of Swabi district in Khyber-Pakhtunkhwa province this afternoon.
The NGO workers were returning from a visit to a community centre.
Five women and a man were killed in the shooting, district police chief Abdul Rashid told the media.
The driver of the car was injured. He was taken to a nearby hospital and was out of danger, Rashid said.
Police have launched a search operation but were unable to trace the attackers.
No group has claimed responsibility for the incident.