This study was an experimental study that examined the relationship between dispositional mindfulness and overclaiming. The hypothesis was that high dispositional mindfulness is associated with lower values of performance for participants in the experimental condition, and that this relationship is mediated by ethical self-concept, how central ethics are to one’s self-concept. Data was collected from a total of 210 participants from the Singapore Armed Forces. Participants completed questionnaires that assessed their dispositional mindfulness, the Stevens’ (1957) magnitude estimation procedure which measured their ethical self-concept, and solved a series a matrices within a time limit. High dispositional mindfulness was associated with greater overclaiming. Moreover, its effect was not significantly mediated by ethical self-concept. This indicates that dispositional mindfulness increases, instead of decreases, overclaiming. Implications of these results are discussed.