Social loafing, i.e. the tendency of some individuals to not exert as much effort in team settings as when they are working alone, has been identified as a major source of productivity loss in brainstorming teams. Studies of social loafing in brainstorming Computer Mediated Communication teams are scant. This paper examines the mechanisms through which previously identified antecedents (Group size and perceived loafing of other members) of social loafing work. This paper utilizes the Theory of Moral Disengagement which helps explain how people engage in antisocial, i.e. social loafing in this case, behavior by disengaging their self-sanctions that otherwise will restrain such conduct. To test the hypotheses, this study employs a controlled experiment with 47 undergraduate students from a Middle Eastern university. Findings indicate that diffusion of responsibility and dehumanization mediates the positive effect of group size on social loafing in brainstorming teams. Also, attribution of blame was found to have a direct negative effect on social loafing. Implications of these findings are discussed and managerial guidelines presented.