The motor-inhibition process was examined in humans by monitoring reaction times (RTs), electromyograms (EMGs), and movement-related potentials. Eight subjects performed two types of visual stop signal paradigm, one with ongoing motor activity and the other without background motor activity. NO-GO-specific negative potentials were consistently recorded from subjects with constant onset and duration relative to the onset of the NO-GO stimulus in both tasks and the spatial distribution of amplitudes was also invariant between the tasks. Sustained background muscle activity was not influenced by the inhibitory command. The constant features of NO-GO-specific potentials during performance of both tasks imply that temporally and spatially similar inhibition processes might specifically suppress the execution of a new motor process without any significant effect on the ongoing motor programme, regardless of differences in preparatory states.