Using the Nambu-Jona-Lasinio (NJL) model we study responses of the pion and kaon masses to changes in the chemical potential, ∂m/∂μ, at zero and finite chemical potential. We find that the behavior of ∂m/∂μ for the pion is quite different from that for the kaon. Our results can give a clue for future studies of ∂m/∂μ on the lattice.