Dispositional mindfulness has emerged in recent years as an important resilience factor that can help to improve mental health, particularly when individuals face stress. However, there has been a lack of longitudinal studies that have examined its role as a moderator of the predictive association between the occurrence of stressors and psychological symptoms. This study examines whether the acting with awareness component of dispositional mindfulness moderates the predictive associations between stressors and several psychological symptoms in a one-year prospective study. An initial sample of 1257 adolescents (ages 14–18) participated in this study. They completed measures of acting with awareness and several psychological problems at baseline and measures of psychological problems and stressors one year later. The results indicate that awareness predicts a decrease in non-suicidal self-injury for automatic and social reinforcement. Moreover, awareness attenuates the predictive association between stressors and both externalizing problems and non-suicidal self-injury behaviors. Although awareness is cross-sectionally associated with lower scores for depressive symptoms and drug abuse, longitudinal associations are not statistically significant.