Although aging is often associated with several negative outcomes (e.g., declines in physical health), older adults generally report more positive and less negative affect than younger adults. The mechanisms underlying this “well-being paradox” are not clearly understood. In the present study, we examined whether differences in trait mindfulness accounted for age differences in affect. Community-dwelling younger (n = 123, Mage = 28.63 years) and older adults (n = 117, Mage = 68.10 years) completed measures of affect and mindfulness. Older adults reported significantly more positive affect and mindfulness than younger adults. Negative affect did not differ by age. After controlling for mindfulness, positive affect no longer differed by age. That is, mindfulness significantly mediated the relation between age and positive affect. An alternative model in which positive affect mediated the relation between age and mindfulness was not supported. These findings suggest that age-related increases in trait mindfulness may contribute to age differences in emotional well-being. Implications of these findings for health and well-being in younger and older adults are discussed.