The purpose of this study was to determine the effect of the changes that occur in the leg muscle activity of unstable surface with different levels of air pressures. Three groups of college students have been placed randomly on unstable surfaces with different air pressures at group 1.0 psi ($n_1$=36), group 1.4 psi ($n_2$=40), and group 1.8 psi ($n_3$=40). Using surface electromyography, the recruitment of the tibialis anterior, peroneus longus, and the gastrocnemius was measured. Maximal voluntary isometric contraction was measured at the different air pressures based on the manual muscle test, then normalizing the value to %maximal voluntary isometric contraction (%MVIC). The tibialis anterior muscle activity was significant change from the unstable surface with difference levels of air pressures between group 1.0 psi and 1.8 psi and between group 1.4 psi and 1.8 psi. peroneus longus muscle activity was significant changes in muscle activity occurred between 1.0 psi and 1.4 psi group and between 1.0 psi and 1.8 psi group. Gastrocnemius muscle activity was significant change in muscle activity occurred between 1.0 psi and 1.4 psi group and between 1.0 psi and 1.8 psi group. In conclusion it identify that 1.0 psi group is most effective on muscle activity than the other groups. These suggest that the rehabilitation or strengthening of patients with ankle injuries, balance exercise with low air pressure like 1.0 psi can be more effective.