A high entropy alloy (HEA) is a multi-component alloy containing several major alloying elements, which has a high degree of atomic disorder that leads to various unique magnetic, mechanical, and electrochemical properties. It is known that one HEA, evaluated previously, is more resistant to general corrosion than type 304 stainless steel (304s), both in H2SO4 and in NaCl solutions at room temperature, but pitting corrosion resistance of the HEA is less than that of 304s. The anodic polarization curves determined for the HEA in aqueous environments showed that the general corrosion resistance of both HEA and 304s decreases as the temperature increases above room temperature. The decrease in the corrosion resistance of the HEA with an increase in temperature is less in NaCl than in H2SO4. The general corrosion rate for the HEA is lower than that for 304s in H2SO4, but higher than that for 304s in NaCl. The activation energies are: 94.06 kJ/mole for the HEA and 219.97 kJ/mole for 304s in 1 N H2SO4, and 310.43 kJ/mole for the HEA and 343.18 kJ/mole for 304s in 1 M NaCl. In addition, it was observed that concentration polarization occurred in cathodic reduction processes in deaerated 1 M NaCl at various temperatures. The polarization curves for the HEA and 304s indicated there is mixed control in 1 N H2SO4 and anodic control in 1 M NaCl based on the assumption that the surface chemical compositions of the two alloys are similar to their bulk chemical compositions. However, the decrease in the cathodic current with time for the HEA at more negative applied potentials is attributed to the high hydrogen overvoltage. In addition, the weak endothermic reaction revealed by differential scanning calorimetry (DSC) analysis showed that only small amounts of Cu-rich phases are segregated in the interdendritic phases; and the wide range of temperatures over which the endothermic reaction occurs indicates the formation of pro-eutectoid phases.