Background & Aims: Social anxiety disorder is one of the most common anxiety disorders. Studying the etiology of this disorder is important. The aim of this study was to evaluate the role of BAS / BIS in social anxiety disorder by mediation effect of cognitive bias.

Materials & Methods: 240 students of Tabriz University were selected by cluster sampling method and then responded to the questionnaire: Scale systems activation / inhibition Carver and White's behavior, revised version of the questionnaire interpretation and Social Phobia Inventory (SPIN). For data analysis, confirmatory factor analysis and structural equation modeling were used.

Results: Evaluation of the structural model using fit indices showed that behavioral inhibition system and behavioral activation system have significant effect on Social Anxiety Disorder by mediational effects of cognitive bias. The results supported the fitness of hypothesis structure between the research variables.

Conclusion: Accordingly, cognitive biases can be a significant mediator between brain-behavioral systems and social anxiety disorder.