The explosion in the town of Salamiya, east of Hama city, occurred hours after a cessation of hostilities came into effect in Syria as part of a US and Russian plan.
It does not apply to Daesh (ISIL) and al Qaeda affiliate the Nusra Front, and the Syrian government and Moscow have said they will not halt combat against those militants. Nusra has called for an escalation of attacks.
The Britain-based Syrian Observatory for Human Rights, which said there was calm in many parts of the country since the agreement came into effect, said the car bomb attack was carried out by Daesh group.
"The car bomb attack is not a breach to the truce because it occurred in an area where the cessation of hostilities agreement does not apply," the Observatory's Rami Abdulrahman told Reuters.
Salamiya is a frontline between government forces and Daesh militants.