Background: Treatment of overactive bladder (OAB) with antimuscarinic agents has been shown to improve depression and/or anxiety symptoms. Objectives: The aim of this study was to evaluate the efficacy of mirabegron on OAB symptoms and its effects on depression and/or anxiety of treatment-naïve women with OAB. Methods: Women treated with mirabegron were prospectively evaluated by the OAB symptom score and hospital anxiety and depression Scale before and at 4 and 8 weeks after treatment. Wilcoxon signed-rank and Spearman rank correlation coefficient were used for statistical analyses, and a p value of < 0.05 was considered as significant. Results: Of the 112 patients who were enrolled, 25.0% had been previously diagnosed as having clinical anxiety and 22.3% as having clinical depression. The OAB, anxiety, and depression symptom scores were significantly improved at both 4 and 8 weeks (p < 0.05). Anxiety, but not depression, symptoms were significantly correlated with OAB symptoms. Conclusion: Improvement of OAB symptoms helps relieve anxiety, but not depression.