The activity of Ag supported zeolite was studied using NO oxidation after atmospheric pressure plasma treatment. The activity of bare zeolite was quite low after O₂ plasma treatment. On the other hand, the Ag supported zeolite had high oxidative activity after treatment. This activity could even be observed a day after treatment. These results indicate the active oxygen fixed on Ag surface by O₂ plasma plays a significant role in the oxidative removal of air pollutants using the plasma-catalyst hybrid system.