We performed ⁷⁵As-NMR measurements in H k ab to investigate the normal-state magnetic properties of CeRh2As2, a recently-discovered heavy-fermion superconductor. We compared the NMR Knight shift K with the magnetic susceptibility χ_ab, and estimated the hyperfine coupling constant A_hf from the slope of the K − χ plot. We observed that the magnitude of A_hf,ab at the As(1) site changes at around 20 K owing to emerging the heavy-fermion state, which was also observed in A_hf at the As(2) site and in H k c. The sign of A_hf,ab at the As(1) site is negative in low temperature. These are important for the analysis of the NMR results of CeRh2As2 in the superconducting state.