Experiencing stressful events that threaten feelings of social belonging can have far-reaching negative impacts on well-being, but there are individual differences in sensitivity to threat that might be explained by dispositional traits. In particular, naturally occurring dispositional mindfulness may be one trait that can explain such differences. To test this possibility, a pool of 495 young adults completed a measure of dispositional mindfulness and a subset of 90 (M = 19 years, SD = 1.3), selected to represent the full range of mindfulness scores, participated in an induced social rejection task (Cyberball). Threat appraisal was collected by asking about perceived exclusion and rejection post-Cyberball, and participants reported their mood and friendliness before, after, and at 3-mins of recovery, and their self-esteem and life meaning after Cyberball and at recovery. Participants higher in mindfulness reported better mood and less unfriendliness prior to Cyberball. Directly after playing Cyberball, a more heightened appraisal of threat, but not mindfulness, was associated with worse mood, less friendliness, lower self-esteem, and less life meaning. Mindfulness directly mitigated the negative effects of rejection on feelings of friendliness post rejection. When mindfulness and threat appraisal were considered in interaction, the association of perceived threat with pre- to post- changes in positive mood and friendliness was strongly negative when mindfulness was high relative to low. Further, mindfulness was associated with better recovery of mood and life meaning by 3-min after Cyberball, and these effects were additive rather than interactive.