Objectives: The aim of this post hoc analysis from the Japanese mirabegron surveillance program was to investigate the safety and effectiveness of mirabegron in male patients with overactive bladder (OAB) symptoms with/without concomitant benign prostatic hyperplasia (BPH). Methods: This 12-week study included patients who were starting mirabegron treatment for the OAB symptoms of urinary urgency, daytime frequency, and urgency urinary incontinence. Patients were stratified according to BPH diagnosis, and patients with BPH were stratified into those who did/did not receive BPH-specific treatment. Assessments included adverse drug reactions (ADRs), residual urine volume evaluations, and total Overactive Bladder Symptom Score (OABSS) and International Prostate Symptom Score-Quality of Life (IPSS-QoL) measurements. Results: Of 4540 male patients, 3176 (70.0%) had been diagnosed with BPH. Mean age was slightly higher in patients with BPH (74.7 ± 8.41 years) versus patients without BPH (71.0 ± 12.13 years). Overall, 66/1364 (4.84%), 170/2588 (6.57%), and 35/569 (6.15%) patients without BPH, with BPH + treatment, and with BPH + no treatment, respectively, experienced ≥1 ADR. No patients without BPH and 21/3176 (0.66%) patients with BPH experienced a urinary retention ADR. No significant changes from baseline to week 12 in residual volume were noted. Mirabegron was judged to be an effective treatment for 990/1296 (76.4%) patients without BPH, 1935/2491 (77.7%) patients with BPH + treatment, and 421/538 (78.3%) patients with BPH + no treatment. Significant decreases in total OABSS and IPSS-QoL were observed for all groups. Conclusions: Mirabegron was a well-tolerated and effective treatment for patients with OAB symptoms with or without BPH in this post-marketing study.