The increasing prevalence of anxiety problems during adolescence underscores the importance of a better understanding of the development of anxiety. While past research has highlighted a link between error responsivity, indexed by error-related negativity (ERN), and youth anxiety, the role of emotion regulation in the ERN-anxiety relationship remains unclear. We conducted a two-wave study with 115 healthy nine-12-year-olds, and found that expressive suppression (ES), an important emotion regulatory strategy, moderates the ERN-anxiety association. A larger T1 ERN predicted heightened T2 anxiety symptoms in those with higher ES. Interestingly, the moderating effect of cognitive reappraisal (CR), another important emotion regulatory strategy, on the ERN-anxiety association was age-dependent; in older youths, the association between T1 ERN and T2 symptoms was significant only for those with lower CR. These findings offer novel insights into the differential age-related patterns in the moderating effects of emotion regulation, and inform future emotion intervention studies for youths.