Previous research has reported that schoolteachers are an at-risk population for stress and anxiety-related psychological disorders. High stress levels have been linked to the suboptimal use of executive functions, abilities which are a major component of effective job performance in educational contexts. In the present study, 99 teachers from five primary schools in Spain were randomly assigned to a mindfulness training group or wait-list control group. All groups were assessed for dispositional mindfulness, anxiety levels, self-reported well-being, and neuropsychological performance (including attention, mental flexibility and inhibitory control, visuoconstructive abilities and visual memory, verbal fluency and processing speed) prior to and following the training program. The results showed significant differences between the groups in terms of dispositional mindfulness, workplace well-being, visuoconstructive abilities, and one of the processing speed indexes. A within-group analysis indicated a general trend toward improvement in the training group, mainly in dispositional mindfulness and verbal fluency. The assessment of neuropsychological performance in this study also contributes to expanding the existing body of knowledge on the effects of mindfulness-based programs using behavioral measures in a research field that heavily relies on self-reported measures.