An electromechanical actuator comprising a frame having mounted thereon a rotary motor and a gear train having an inlet shaft lying on the same axis as an outlet shaft of the motor and connected thereto, and an outlet ring coaxial with the outlet shaft of the motor and connected to a lever for operating a member that is to be driven. The gear train is carried by a casing mounted on the frame to pivot about the axis of the outlet shaft of the motor. An anti-blocking device is mounted on the frame and comprises a movable element that is movable between a blocking position for blocking the casing in rotation relative to the frame, and a release position for releasing the casing in rotation relative to the frame.