The corrosion behavior as well as the electrochemical surface response of the novel CoCrFeMnNi (marked A1H) high entropy alloy (HEA) prepared by mechanical alloying of Co, Cr, Fe, Mn, Ni powders combined with Hot Isostatic Pressing (HIP: 1000 degrees C/15 min/150 bar) has been studied in chloride environment. Moreover, combination of the powder metallurgy and HIP allows to obtain HEA Metal Matrix nano-Composite (MMnC) with SiC nanoparticles addition as a reinforced phase. The influence of 5 %wt. SiC nanoparticles addition (specimen marked A1H5SiC) in A1H has been also investigated. Polarization tests indicate both passivation properties and pitting susceptibility of A1H alloy. This has been confirmed by the corrosion potential (OCP) and the electrochemical impedance spectroscopy measurements (EIS) which revealed strong passivation process in the first 16 h of immersion in 0.1 M NaCl water solution. The addition of 5 wt% of SiC nanoparticles improves the mechanical properties (e.g. hardness, yield stress) simultaneously changing the surface electrochemical response by the time reducing (from 16 h to 4 h) of the corrosion resistance during immersion in chlorides.