The gunmen ambushed the car near the remote Sher Afzal Banda area of Swabi district in Khyber-Pakhtunkhwa province.
The NGO workers were returning from a community centre.
Six women and a man were killed in the shooting, district police chief Abdul Rashid told reporters. The driver of the car was injured.
He was taken to a nearby hospital and was out of danger, Rashid said.
The victims worked for the NGO Ujala that is engaged in health and education programmes.
Four gunmen were involved in the attack, officials said.
Police have launched a search operation but were unable to trace the attackers. No group has claimed responsibility for the incident.
The police said they were investigating whether there was any link to the Taliban or other Islamist militants, who have been blamed for past attacks on charity workers and on health education projects.
The Pakistani Taliban have banned polio vaccinations in restive Waziristan, saying that the campaign was a cover for espionage after the jailing of a doctor who helped the CIA find Osama bin Laden using a hepatitis vaccination programme.
In December, nine polio vaccination workers were shot dead in a string of attacks in Karachi and the northwest.
Though the Taliban denied responsibility for the killings, the deaths prompted the UN children's agency and the World Health Organization to suspend work on polio campaigns.