Although substantive research has shown that a positive perceived school climate is an essential protective factor for cyberbullying among adolescents, little research revealed the mechanisms underlying this relationship. This study examined whether normative beliefs about aggression mediate the association between a positive perceived school climate and cyberbullying and whether this process is moderated by Internet morality. Anonymous questionnaires measuring these variables were administered to 649 junior high school students in China. After controlling for traditional bullying, mediation analysis indicated that normative beliefs about aggression played a full mediating role in the relationship between a positive perceived school climate and cyberbullying. Moderated mediation analysis further revealed that Internet morality moderated the predictive effect of normative beliefs about aggression on cyberbullying. The mediating effect of normative beliefs about aggression was stronger in individuals with lower levels of Internet morality. These findings provide insight into making existing interventions more suitable for cyberbullying.