 Manganese oxides (MnOx) are expected to be highly active catalysts for O2 electroreduction. However, MnOx are prone to aggregation, thus reducing their catalytic active sites. Herein, a composite of spherical MnO2 coated with reduced graphene oxide (denoted as MnO2@RGO) was fabricated by a facile and green step galvanostatic electrodeposition. The obtained MnO2@RGO is composed of a RGO lamina shell (10 nm) and spherical MnO2 core (100 nm), which were confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Brunner–Emmet–Teller (BET) measurement, Raman, and X-ray photoelectron spectroscopy (XPS). The obtained composite exhibited a high specific surface area of 251.3 m2 g−1. The as-prepared MnO2@RGO composite displayed a more positive onset potential of 0.86 V vs. reversible hydrogen electrode (RHE), higher kinetic current density (11.23 mA cm−2 at 0.2 V), and higher electron transfer number in OH− solution (n ≈ 3.94) for oxygen reduction reaction (ORR) compared to MnO2 NPs scattered on the surface of RGO (MnO2/RGO), bulk MnO2 NPs, and RGO. The enhanced activity was further demonstrated by the lower Tafel slope (72 mV dec−1). Moreover, MnO2@RGO exhibited greater “tolerance to methanol,” “anti-CO poisoning” ability, and catalytic stability compared to commercial Pt/C catalyst. The results indicated that the prepared MnO2@RGO composite can be a potential low-cost and effective electrocatalyst for ORR.