Apart from being defined as a state achieved during meditative practices, mindfulness is also conceptualized as a dispositional trait - the tendency of the individual towards mindful behavior and mindful experiences in everyday life. Dispositional mindfulness (DM) is generally measured by self-report. However, the first behavioral measure - Breath Count Task (BCT), which circumvents many biases typical of self-report measures, has recently been developed. The aim of the present study was to clarify the relationship between videly used self-report measure – FFMQ and the behavioral measure (BCT) of DM and to compare their convergent and predictive validity on a sample of 76 psychology students of the Faculty of Humanities and Social Sciences in Rijeka, aged between 18 and 26. To assess convergent validity, the association of FFMQ and BCT was examined, as well as the association of these measures with self-reported mind-wandering and neuroticism. Research to date has confirmed the association of DM with working memory, as well as with a number of socioemotional outcomes. Therefore, the Change Detection Task with emotional facial expressions was used to assess the predictive validity of DM. The research procedure consisted of online questionnaire completion and individual experimental probes in laboratory settings. The results show a lack of correlation between FFMQ and BCT. Furthermore, FFMQ and BCT did not predict individual's performance in the Change Detection Task, with the exception of the Acting with Awareness facet, which showed a marginally significant negative correlation with performance on the task. Contrary to expectations, individuals who were more accurate in detecting changes in facial expressions appear to report less acting with awareness. High negative correlations were observed between the total score on FFMQ, as well as individual facets, and mind-wandering and neuroticism. An association of miscounts in the first half of BCT with results on neuroticism was obtained. Contrary to the given hypothesis, fewer miscounts were associated with higher scores on neuroticism. Important contribution of the current research is made by independent assessments of breathing, which were used for the first time in BCT and proved to be significantly related to the respondents' reports of breathing. The absence of expected correlations between constructs is explained with DM construct validity issues and methodological shortcomings of the research itself.