This study explored the neural basis of the processing of anomalous information (the N400 effect) in an arithmetic task. Twenty healthy undergraduate students were scanned while they performed a number-matching task. Relative to matched numbers, unmatched numbers elicited significantly greater activation at left inferior and superior parietal cortex, left inferior frontal gyrus, and left fusiform and lingual gyri. Combining these results and those of previous studies on semantic anomaly, we proposed that the parietal region is the source of the arithmetic N400 component and the left inferior frontal gyrus is involved in domain-general processing of anomalous information.