Workplace well-being has received considerable attention over the past decade. Relative to the positive relationship between affective well-being and in-role performance, the relationship between affective well-being and extra-role performance has received little empirical attention. The purpose of this study was to examine the relationships among affective well-being, work engagement, collectivist orientation, and organizational citizenship behavior. Specifically, we tested this model with a sample of 264 employees from a telecom company in China. We found that: (1) affective well-being was the positive predictor of organizational citizenship behavior ( = 0.482, < 0.001); (2) work engagement mediated the relationship between employee affective well-being and organizational citizenship behavior (indirect effect = 0.330, < 0.001); and (3) collectivist orientation moderated the relationship between affective well-being and work engagement ( = 0.113, < 0.01) and affective well-being and organizational citizenship behavior ( = 0.084, < 0.05). Our discussion highlights the benefits of understanding the role of work engagement and cultural values with regard to the relationship between affective well-being and organizational citizenship behavior.