Researchers have revealed that comparing the perceptual input with the representations stored in visual working memory initiates a rapid attention-shift, which is predominantly triggered by the relevant-feature change. The comprehension of the change contents further necessitates a follow-up comparison that contrasts all the object features regardless of the task relevancy. However, whether such a distinct stage exists and how the process is carried on need further verification. We explored this issue by investigating the underlying neural mechanisms of the percept–memory comparison. By recording EEG, we found that both the task-relevant and -irrelevant feature changes elicited significantly more negative anterior N2 waves (230–340ms) rooting in the anterior cingulate cortex (ACC), and meanwhile activated the frontal theta (5–8Hz, 250–550ms). These results suggest that a distinct comparison stage does exist, which is supported by the anterior N2, ACC and frontal theta.