This study examined the effects of exposure to the electromagnetic field emitted by mobile phone on human cognitive function. Total volunteers were twenty and volunteers were separated in two groups. One is teenager group, and the other is adult group. Test was performed in the counterbalanced order(sham-real, real-sham). Subject remained blind to mobile phone status during the exam. The result showed that the exposure to the electromagnetic field significantly speeded up response time fur teenager group. This results suggest that exposure to the electromagnetic field emitted by cellular phones may have a mild facilitating effect on cognitive function in teenager group.