Anxious youth may experience altered positive affect (PA) relative to healthy youth, perhaps because of greater sensitivity to social experiences. Altered PA may be especially evident during the transition to adolescence, a period in which positive social events increase in salience and value. The current study evaluated whether anxious youth show differences in baseline PA, rate of return to baseline, and variability around baseline PA and tested whether these differences would depend on social context and anxiety subtype. Participants were 176 9- to 14-year-old youth, including 130 clinically anxious (with Social Anxiety Disorder, Generalized Anxiety Disorder, and/or Separation Anxiety Disorder) and 46 healthy youth. Youth reported their current PA, peak PA in the past hour, and social context in natural settings using ecological momentary assessment. Hierarchical linear models showed that both socially anxious and other anxious youth showed greater variability of PA relative to healthy youth. Youth with other anxiety disorders showed higher peak PA to a positive event relative to healthy youth. Feeling close to a friend was associated with higher peak PA, especially for socially anxious youth. Socially anxious youth showed significantly lower peak PA relative to both healthy and other anxious youth when interacting with a less close peer, but similar levels to these youth when interacting with a close friend. These findings suggest that clinically anxious youth may more sensitive to positive events and social interactions than healthy youth. Findings provide potential treatment targets for anxious youth, including applying regulatory strategies to positive events.