Purpose: This study is based on the JD‐R model and aims at understanding the role of work engagement (WE) as a mediator between job resources (i.e. perceived organizational support) and positive extra‐role behaviors (i.e. organizational citizenship behaviors (OCB)), between job demands (i.e. interpersonal conflicts at work) and negative extra‐role behaviors (i.e. counterproductive work behaviors (CWB)), and also between a personal resource (i.e. conscientiousness) and both types of extra‐role behaviors.Design/methodology/approach: Data from three Romanian organizations (n=258) were collected in a cross‐sectional study. Two main models (fully mediated and partially mediated) tested the role of WE as a mediator, using structural equation modelling.Findings: The results support the partially mediated model. All anticipated antecedents have a direct, and also an indirect relation with extra‐role behaviors – via WE. In addition, the mediating effect was stronger for OCB than for CWB. Overall, the results show that job and personal characteristics differentially predict OCB and CWB, and that employees' affective‐motivational state explains, in part, these job and personal characteristics – extra‐role behaviors associations.Originality/value: The paper advances the knowledge about the JD‐R model and its relevance for OCB and CWB. In addition, understanding work engagement's potential to stimulate OCB and inhibit CWB can aid professionals to advance beneficial behavioral outcomes in organizations by promoting wellbeing at work, thereby supporting the employees' healthy career development.