Oxygen evolution reaction (OER) is the key step involved both in water splitting devices and rechargeable metal-air batteries, and hence, there is an urgent need for a stable and low-cost material for efficient OER. In the present investigation, Co-Fe-Ga-Ni-Zn (CFGNZ) high entropy alloy (HEA) has been utilized as a low-cost electrocatalyst for OER. Herein, after cyclic voltammetry activation, CFGNZ-nanoparticles (NPs) are covered with oxidized surface and form high entropy (oxy) hydroxides (HEOs), exhibiting a low overpotential of 370 mV to achieve a current density of 10 mA/cm² with a small Tafel slope of 71 mV/dec. CFGNZ alloy has higher electrochemical stability in comparison to state-of-the art RuO₂ electrocatalyst as no degradation has been observed up to 10 h of chronoamperometry. Transmission electron microscopy (TEM) studies after 10 h of long-term chronoamperometry test showed no change in the crystal structure, which confirmed the high stability of CFGNZ. The density functional theory (DFT) based calculations show that the closeness of d(p)-band centers to the Fermi level (E_F) plays a major role in determining active sites.This work highlights the tremendous potential of CFGNZ HEA for OER, which is the primary reaction involved in water splitting.