We examined the effects of complexity on the efficiency of pattern encoding in the general population differing on autism-spectrum quotient (AQ) scores. We compared brain activity (electroencephalography) during a same-different task for High and Low AQ groups. The task was composed of identical comparison and categorical comparison (CC) conditions that presented simple or complex patterns. In the CC condition, the Low AQ showed large P3b amplitudes with simple patterns than with complex patterns, whereas the High AQ showed the same amplitude levels for these patterns. These indicate that, similar to simple patterns, complex patterns are efficiently encoded in the High AQ. Moreover, the High AQ had no impairment in the global pattern encoding compared with the Low AQ.