[Purpose] This study compared the T10 and L4 paraspinal muscle activities over time during continuous computer work. [Subjects] Ten male workers participated in this study. [Methods] The T10 and L4 paraspinal muscle activities were measured using a surface EMG system after 0, 20, 40, and 80 minutes of continuous computer work. [Results] The T10 and L4 paraspinal muscle activities after 20 and 40 minutes were increased significantly compared with the initial values, while they were decreased significantly after 80 minutes compared with the initial readings. [Conclusion] This study suggests that workers using computers for short periods would benefit from back muscle stretching exercises due to increased tension in these muscles. For longer computer work, strengthening exercises would be more effective than stretching due to decreased back muscle activation.