The aim of this study was two-fold: to investigate the relationship between emotion regulation, dispositional mindfulness and bullying/victimization experiences at school, and to examine the mediating effects of internalizing and externalizing problems on this relationship. Self-reports measuring the above variables were completed by 444 adolescents (mean age 15.3) who attended high school in Cyprus. Data were collected at three points in time. Specifically, data were collected during the second week of October, 2018 (T1), the third week of January, 2019 (T2) and the first week of June, 2019 (T3). It was found that mindfulness at T1 had a significant negative effect on both internalizing and externalizing symptoms and through these variables, it had an indirect negative effect on both bullying and victimization at T3. Similarly, adaptive emotion regulation at T1 had an indirect effect on victimization, fully mediated by internalizing problems. In contrast, maladaptive emotion regulation had a positive, direct effect on both bullying and victimization.