Introduction: Obsessive-compulsive disorder (OCD) affects 1.1–1.8% of the population, and adult females are more likely to suffer from it. Deep transcranial magnetic stimulation (dTMS) targets the hyperactivity of the dorsomedial prefrontal cortex and anterior cingulate cortex – two frontal brain networks implicated in OCD. This study aims to identify a biological marker for beta rhythm that correlates with the treatment response works following dTMS. Methods: A total of 56 right-handed treatment-resistant OCD patients (35 female and 21 male) were retrospectively included in the study which were treated with FDA-approved dTMS protocol by using H7-coil for OCD. The Yale-Brown Obsessive Compulsive Scale (Y-BOCS) was used before and after dTMS to determine the severity of OCD symptoms and the responsiveness to therapy. To record the quantitative electroencephalogram (QEEG), 19 electrodes were applied to the scalp. Results: When controlling for sex and age, the Y-BOCS decline rate was linked to higher pretreatment beta activity in the parietal and occipital regions. In the second step of our attempt, we used stepwise linear regression analysis to create a model to predict YBOCS decline rate, age (beta = -0.284, p = 0.030) and pretreatment beta parietal power band (beta = 0.312, p = 0.018) were the predictors. Conclusion: Age and pretreatment parietal beta power bands may be used as a biomarker for predicting response to dTMS therapy if confirmed by further studies.