A microwave-excited atmospheric pressure plasma jet (ME-APPJ) was generated utilizing coaxial transmission line resonators with the resonance frequency of 788 MHz. We investigated the effects of the operating parameters such as input power and gas flow rate on the electron excitation temperature and electron density using optical emission spectroscopy. The amounts of various reactive species in the plasma-activated media (PAM) exposed by the ME-APPJ were estimated using colorimetric methods. The PAM was applied to A549 cultured cells and subsequently incubated for a given duration. The concentrations of NO2- and H2O2 in the PAM incubating A549 cells were monitored until 24 h. The reduced cell viability rate was observed on A549 cells incubated in the PAM. The concentrations of NO2- and H2O2 and the viability of A549 cells depended on the operating conditions of ME-APPJ. The cell viability rate exhibited a decrease with increasing power and decreasing gas flow rate. Correlation between the concentrations of gaseous reactive species in the plasma and in the PAM and the cell viability is discussed.