This study investigates the psychological effects of social identity on both posters and lurkers in online brand communities (OBCs). The results reveal the intermediate mechanisms mediating and moderating members’ social identity effects on members’ brand commitment, leading to positive word‐of‐mouth and their resistance to negative information about the brand. This article treats social identity as a multidimensional construct. Differences between posters and lurkers on the relationships among the cognitive, affective, and evaluative components of social identity are investigated along with their positive effect on brand commitment and behavioral consequences. Using a sample of 752 OBC members, both posters and lurkers emerge as valuable members and equally likely to derive social identity from their membership of an OBC. However, there are counterintuitive results for relationships within the research model between active and passive members of OBCs. These results offer implications for theory and can help managers to be better interactive marketers.