Little is known about the mechanisms through which mindfulness is related to psychological symptoms such as anxiety. One potential mechanism consists of individual differences in emotion-responding variables such as reactivity to aversive stimuli. The current research was designed to examine whether affective reactivity may act as a mechanism of mindfulness. Across two studies, an inverse relation between trait mindfulness (specifically, the Nonjudging of Inner Experience and Acting with Awareness factors of the Five-Facet Mindfulness Questionnaire) and chronic anxiety was partially mediated by affective reactivity, assessed with direct (self-report in study 1) and indirect (lexical decision task in study 2) measures. These results contribute to the understanding of the psychological mechanisms through which mindfulness works.