Our goal was to test a model of sociopolitical attitudes that posits a relationship between individual differences in liberal versus conservative political orientation and differential levels of anterior cingulate cortex (ACC) responsivity. We recorded event-related potentials (ERPs) while participants who varied along a unidimensional liberal-conservative continuum engaged in a standard Go/NoGo task. We also measured component attitudes of political orientation in the form of traditionalism (degree of openness to social change) and egalitarianism (a preference for social equality). Generally, participants who reported a more liberal political orientation made fewer errors and produced larger ACC-generated ERPs (the error-related negativity, or ERN and the NoGo N2). This ACC activation, especially as indicated by a larger NoGo N2, was most strongly associated with greater preference for social equality. Performance accuracy, however, was most strongly associated with greater openness to social change. These data are consistent with a social neuroscience view that sociopolitical attitudes are related to aspects of neurophysiological responsivity. They also indicate that a bidimensional model of political orientation can enhance our interpretation of the nature of these associations.