The present invention relates to an electromechanically operated disc brake for motor vehicles, which consists of a floating-type brake caliper as well as an actuating unit arranged on the caliper. The actuating unit exhibits an electric motor which adjusts an actuating element via a reducing gear. The actuating element in turn causes one of two friction linings provided in the brake caliper in a displaceable manner to be brought into engagement with a brake disc. In order to be able to maintain high clamping forces with very low electric power, the present invention proposes that means (20 or 21,22) be provided to prevent reverse rotation of the rotor (10) of the electric motor (6) when the current supplied to the electric motor (6) is switched off after said electric motor (6) was activated. At the same time, this measure minimizes heating of the electric motor.