A portable seat assembly includes a frame that may be removably mounted in a vehicle. A plurality of retention units is provided and each of the retention units is attached to the frame. Each of the retention units may engage an inside surface of an exterior wall of the vehicle thereby retaining the frame in an upright position. A lock is attached to one of the retention units. The lock may engage the inside surface of the exterior wall of the vehicle thereby preventing the retention units from being dislodged from the interior surface of the exterior wall of the vehicle. A seat is coupled to the frame and the seat may be sat upon.