Background : The purpose of the study was: to investigate muscle activation of upper arm according mouse shape. Methods : Twenty person(mean age : 23. 7) who have healthy condition was participated this study, we collected data of muscle activation using by EMG from upper trapezius(Tr), deltoid middle fiber(De), extensor digitorum(Ed), first dorsal interosseous(Di) during participants was performed click and drag according various mouse. Mouse shape was divided 4 level as follow shape 1 was very small, 2 was small, 3 was moderate, 4 was large. Data was analyzed ANOVA, independent t-test using by SPSS ver18.0. Results : There was significantly difference of muscle activation among each muscle according mouse shape in drag and click. In shape 1, 4, there was significantly difference of muscle activation of Tr, De, Ed between drag and click except Di. In shape 2, 4, there was significantly difference of muscle activation of all muscle between drag and click. Conclusion : We knew that extensor digitroum showed more higher muscle activation than other muscle in drag, first dorsal interoseous showed more higher muscle activation that other muscle in click. We suggest that mouse shape was very important factor in order to prevent skeletal muscular disorder for computer user, and mouse shape can reduce muscle fatigue during computer work.