The cars were parked in a grassy field at the Robinson Family Farm's fall festival celebration on Saturday.
According to the Bell County Fire Marshal's Office, it is believed the blaze was sparked by a cigarette that someone threw in the dry grass.
Bell County is currently under a burn ban because of extreme drought conditions.
Fortunately, no one was injured.
The farm is family owned, and according to its website, opens seasonally for Easter, a pumpkin patch and for precut Christmas tree sales.