We investigated potential correlations between underlying electroencephalogram (EEG) spectral power and aggressive or nonaggressive antisocial behavior. Frontal and parietal EEG spectral properties were calculated for 3 different ranges (theta, 4–8 Hz; alpha, 8–10.5 Hz; and beta, 10.5–30 Hz) in 900 twins in an open-eyed resting state during 2 stages of development: ages 9–10 and ages 14–15. In multilevel regression modeling, relationships emerged between EEG spectral power properties and measures of antisocial behavior at age 14–15 years but not at the concurrent age of 9–10 years, providing support for neurodevelopmental underpinnings for adolescent-onset antisocial behavior. For boys, frontal alpha power, frontal beta power, and parietal beta power were correlated with aggressive antisocial behavior. For girls, parietal alpha power was anticorrelated with nonaggressive antisocial behavior, raising questions about differing neurobiological profiles for antisocial behavior between sexes. These results also support a distinction between aggressive and nonaggressive antisocial behavior.