Validation of self-report mindfulness measures has been promising, although comparisons with non-self-report instruments are lacking. Because past research suggests that mindfulness training is associated with improved attention, this study predicted that higher self-report mindfulness would be positively related to performance on tasks of sustained attention. Fifty undergraduates completed the Mindful Attention Awareness Scale (MAAS), the Kentucky Inventory of Mindfulness Skills (KIMS), the Cognitive and Affective Mindfulness Scale, Revised (CAMS-R), and performed the Continuous Performance Test II (CPT-II) and the Paced Auditory Serial Addition Test (PASAT). Mindfulness scores, as measured by the MAAS and CAMS-R, were negatively related to target omissions on the CPT-II (ps ≤ 0.001), but were not related to PASAT performance (ps ≥ 0.11). Scores on the KIMS were not related to the CPT-II or PASAT (ps ≥ 0.15). Results suggest that self-report mindfulness is related to exaggerated lapses of attention, as measured by the CPT-II.