Many anxiety disorders begin in adolescence. Early interventions that target adolescent anxiety may prevent later disabling consequences. Previous studies show that cognitive bias modification training can generate positive interpretative styles of ambiguous information in adolescents but effects on anxious mood reduction are less clear. Adult studies suggest more consistent training effects on mood when assessed in response to a psychological challenge. Here, we assess whether positive training reduces adolescent anxious responses to a laboratory stressor. A total of 40 adolescents were randomly assigned to positive or negative computerised training. During training, ambiguous scenarios were resolved positively or negatively. After training, adolescents completed a test of interpretation bias and a difficult mental arithmetic task while believing that they were being videotaped for teaching purposes. First, positively-trained adolescents endorsed more positive and fewer negative interpretations of new ambiguous situations than negatively-trained adolescents. Second, positively-trained adolescents also showed attenuated anxiety levels after but not before the challenge. Induced positive interpretations via computerised cognitive training may modify anxious responsivity. Although there are some caveats to these data, in general they justify extensions of computerised training to adolescents with clinical anxiety, to reduce anxious responsivity.