Previous studies showed that the anterior cingulate cortex (ACC) is activated when individuals engage in attention and inhibitory control tasks. The present study examined whether ACC activity is associated with behavioral performance of the two tasks. Twenty normal and 20 children with autism spectrum disorders (ASDs) were subjected to neuropsychological assessments on attention and inhibitory control, as well as electroencephalography recording. Children with ASD performed significantly worse than normal children on attention tasks as shown in their poorer performance on the Digit Span test, the greater number of Omission Errors on both the Continuous Performance Test II and the Go/No-Go tasks. They also performed significantly worse than normal children on inhibitory control tasks as shown by the greater number of False Alarms on the Object Recognition and Hong Kong List Learning Test. Their ACC activities, as indicated by relative theta power, were found to be significantly lower than those of normal controls during performance of the Go/No-Go task. Depressed ACC activities were further found to be significantly associated with poorer performance in attention and inhibition. Clinical implications on the use of theta activities in the ACC as an indicator to monitor intervention progress in children with ASD were discussed. (Contains 3 figures and 4 tables.)