As smartphone usage has increased recently, so has smartphone addiction. Many of the smartphone users, however, do not even recognize the risk of smartphone addiction. In this experiment, smartphone users have been categorized into two groups by smartphone addiction measure (S-measure) developed by 2011 National Information Society Agency (NIA): A high risk group and a normal group. The changes of brain waves have been observed when the subjects were watching emotional videos of anger, sadness, happiness, and fear. The results show that the values of FP1 and FP2 (frontal lobe) theta band of the high risk group have been measured to be high, which indicate anxiety disorder. Although happiness and fear videos showed no difference between these groups, sadness and anger videos showed significantly different results for these groups: the brain waves of the high risk group showed higher values than those of the normal group. Therefore, this experiment showed that the high risk group takes feelings of sadness and anger more sensitively than the normal group.