The S1-S2 go/no-go reaction time task has been frequently used to assess volitional inhibition. In this study our aim was to compare the ERPs elicited by S1 and S2 by using a modified S1-S2 paradigm which involved a two-stage go/no-go decision. The go and the no-go S1 ERPs did not differ substantially, and both displayed a prominent negativity with peaks at 260 ms (S1N260) and at 330 ms (S1N330) post-S1. The S1N260 was similar to the N2 from no-go S2 trials. Since after all three types of stimuli, movement is not required and is inappropriate, this negativity may represent the correlate of the voluntary decision to suppress movement. Later, the S1 ERPs were dominated by frontal negativity (S1N330), probably reflecting further processes related to response preparation, while the S2 ERPs displayed a large central and parietal positivity (P3), probably reflecting the processes of evaluation of response accuracy.