Previous research has indicated that organizational justice perceptions can reinforce Organizational Citizenship Behaviors (OCBs). However, little attention has been paid to the role of the facets of organizational justice and their unique contribution to OCBs. Furthermore, the mechanisms that potentially explain this relationship are unclear. The first aim of this study was to investigate the relationship between multifocal organizational justice facets (i.e., distributive, procedural, and interactional) and OCB levels focusing on interpersonally focused (OCBI) and organizationally focused (OCBO). Second, the study examined whether psychological capital mediates the organizational justice-OCB relationship. Employees working in an Iranian oil company (n = 200) were analyzed through structural equation modeling. The results demonstrated that from the facets of organizational justice, interactional justice was positively associated with interpersonally focused (OCBI). Moreover, psychological capital mediated the relationship between procedural justice and citizenship behaviors at both OCB levels. The results suggest that increasing OCB among employees is not only a social interaction phenomenon but also includes employees’ instinct motivation aspects. Therefore, granting employees enough authority and control over their jobs and communicating with them based on appreciation will create better circumstances to exhibit prosocial behavior.