There is growing concern over the emergence of damaging compulsive use patterns among some users of social networking sites (SNSs), in particular of mobile social media. Although previous studies argue that mindfulness has a protective effect on compulsive behaviors, to date, no study has analyzed the underlying mechanisms by which mindfulness reduces compulsive SNS usage. This study addresses this gap by examining the relationship between mindfulness, self-esteem, social anxiety, compulsive mobile SNS usage, and derived stress in the context of the use of the mobile social media application, WhatsApp™. Mediation analysis supported the roles of self-esteem and social anxiety as mediators of the beneficial (lowering) effect of mindfulness on compulsive mobile SNS usage. Moreover, the results confirmed that compulsive mobile SNS use induces stress and that mindfulness has also lowering effects on stress derived from such compulsive behavior, mediated by the former variables. This research, therefore, provides a process explanation for the beneficial effect of mindfulness on stress derived from mobile social media use. Further theoretical and practical implications, as well as future research avenues, are discussed.