The aim of the study was to explore the psychophysiological concomitants of self-reported behavioral inhibition system (BIS) sensitivity in adolescents (12 to 17 years old) supposed to be at risk for anxiety disorders. Twenty participants with high scores in self-reported BIS sensitivity (at-risk group) were matched in age and sex to 20 participants scoring in the normal range in BIS sensitivity (control group). Negative affect, negative emotion regulation style, and anxiety symptomatology were assessed by means of self-reported measures. Cardiac and electrodermal response signals were recorded during baseline, paced breathing, exposure to an attentional task with response cost and fear-relevant slides conditions. The at-risk group exhibited higher scores on measures of negative affect, negative emotion regulation style, and anxiety symptomatology than their control counterparts. After controlling for negative styles of emotion regulation, groups did not differ in skin conductance reactivity during the attentional task with response cost, but participants at risk exhibited more nonspecific skin conductance responses than the control group during baseline recording. Regarding the cardiac concomitants, participants at risk presented lower vagal tone at resting conditions as compared to participants in the control group. Additionally, at-risk participants exhibited lower flexibility across experimental conditions in heart rate and cardiac sample entropy measures than participants in the control group. These findings add knowledge on psychophysiological concomitants of BIS sensitivity and are discussed in light of associations between temperament and development of anxiety disorders in youth. They show how psychophysiological patterns observed in resting conditions could be useful endophenotypes to reliably detect individuals at risk before the disorder onset.