We report on an all-electrical locking of the optical frequency of a distributed feedback laser diode at 1548 nm tunable over 9 nm on a fibered Fabry-Perot cavity. We demonstrate a 7-MHz servo bandwidth and a frequency noise suppression down to 10 Hz/root Hz at 200-kHz carrier offset frequency in the error signal. From this signal, we estimate the laser linewidth to be 100 Hz at a 10-ms integration time. This stabilized laser will be a component of a compact source of continuous millimeter or submillimeter low phase noise electrical waves.