Recent theories suggest that error is detected based on the process generating an appropriate response from the presented stimulus, including stimulus processing (e.g. encoding and evaluation) and activation of the appropriate response. This study examines the effects of stimulus processing (related to stimulus deviance) and activation of the appropriate response on error-related negativity (ERN/Ne). We administered a three-choice-response task, in which participants were asked to respond with a finger corresponding to the presented stimulus. The stimuli consisted of three letters, one of those was presented with low probability (20%) and the others were presented with high probability (40%) each. Using error-correcting responses, we estimated the degree to which the appropriate response is activated. The error-correcting response was faster on the high-probability rather than the low-probability trials, suggesting that the appropriate response was more active immediately after an error on the high-probability trials. However, the ERN/Ne amplitude was not larger on the high-probability as compared with the low-probability trials. Moreover, we found an increase in ERN/Ne amplitude on the low-probability trials, in which N1 was enhanced with regard to stimulus deviance. These results suggested that ERN/Ne is associated with stimulus processing rather than activation of the appropriate response.