In this paper, using the optical emission spectroscopy (OES) technique, the optical characteristics of a radiofrequency (RF) plasma jet are examined. The $\rm{Ar/O_2}$ mixture is taken as the operational gas and, the Ar percentage in the $\rm{Ar/O_2}$ mixture is varied from 70% to 95%. Using the optical emission spectrum analysis of the RF plasma jet, the excitation temperature is determined based on the Boltzmann plot method. The electron density in the plasma medium of the RF plasma jet is obtained by the Stark broadening of the hydrogen Balmer $H_\beta$. It is mostly seen that, the radiation intensity of Ar $\rm{4p\rightarrow 4s}$ transitions at higher argon contributions in $\rm{Ar/O_2}$ mixture is higher. It is found that, at higher Ar percentages, the emission intensities from atomic oxygen (O) are higher and, the line intensities from the argon atoms and ions including O atoms linearly increase. It is observed that the quenching of $\rm{Ar}^\ast$ with $\rm{O}_2$ results in higher O species with respect to $\rm{O}_2$ molecules. In addition, at higher percentages of Ar in the $\rm{Ar/O_2}$ mixture, while the excitation temperature is decreased, the electron density is increased.