Although personality and culture have been employed as independent predictors of emotion regulation, less is known about the interplay between them. Thus, the present study tests their interaction by focusing on the match between personality (public self-consciousness) and culture (valuing independence vs. interdependence) in modulating an emotion regulation strategy, namely, emotion suppression, on Facebook. Furthermore, relationship concern related to the expression of positive and negative emotions on Facebook is explored as a potential underlying mechanism. An online survey on Facebook users in the United States (n = 320) and South Korea (n = 336) was conducted through two professional survey companies. The results revealed that the positive association between public self-consciousness and emotion suppression was stronger among respondents who value interdependence (vs. independence), which led to a significant interaction between the two predictors. Furthermore, public self-consciousness was associated with emotion suppression through relationship concern for the expression of positive, but not negative, emotions. Furthermore, this mediated relationship was stronger among respondents who value interdependence (vs. independence). Lastly, the study discussed the importance of exploring the interplay between personality and culture and the implication of dialectic emotions.