A lockable electromechanical actuator including: a screw extending along a longitudinal axis; a nut engaged on the screw and provided with means for connection to an element that is to be moved; and a passive locking device for locking the element that is to be moved in the retracted position; the passive locking device including a device for actuating a lock that can selectively adopt a first position in which the lock prevents relative turning between the screw and the nut, which would lead to the element that is to be moved being deployed, and a second position in which the nut is free to turn, the lock passing from one of its first and second positions to the other one of its first and second positions when the element that is to be moved is taken beyond its retracted position.