Recent work suggests that a generalized error-monitoring circuit, which shows heightened activation when one commits an error in goal-directed behavior, may exhibit synonymous activity when one watches another person commit a similar goal-directed error. In the present study, fMRI was utilized to compare and contrast those regions that show sensitivity to the performance, and to the observation, of committed errors. Participants performed a speeded go/nogo task, and also observed a video of another person performing the same task. Dorsal anterior cingulate, orbitofrontal cortex, and supplementary motor regions were commonly activated to both performed and observed errors, providing evidence for common neural circuitry underlying the processing of one's own, and another's mistakes. In addition, several regions, including inferior parietal cortex and anterorostral and ventral cinguli, did not show activation during performed errors, but were instead uniquely activated by the observation of another's mistakes. The unique nature of these 'observer-related' activations suggests that these regions, while of potential import towards recognition of another's errors, are not core to circuitry underlying error-monitoring. Rather, we suggest that these regions may represent components of a distributed network important for the representation and interpretation of complex social actions.