Exoskeletons have been used successfully for functional training of human motions. Our designs of the Cable-driven Arm Exoskeleton (CAREX) are targeted to improve arm function in patients with stroke. In this study, we focus on how muscle activation patterns of subjects change during movements with and without CAREX. Our goal was to evaluate whether CAREX distorts the natural pattern of EMG activity in healthy human subjects during arm movements. Eight healthy subjects performed point-To-point reaching tasks under two conditions: (a) with or without CAREX, and (b) with or without a 5 lb weight attached to their wrist. The EMG signals of 10 muscles were recorded and processed. The results showed that (i) EMG pattern of the subjects while wearing CAREX and while not wearing CAREX showed a high correlation, suggesting little alteration to normal EMG patterns while wearing CAREX; (ii) The subjects showed significantly lower muscle activation when they wore CAREX; (iii) The high correlation and the lower activation were observed in both the no weight condition and the 5 lb weight condition. Overall, the results suggest that CAREX can help subjects reduce the magnitude of muscle activation while preserving normal muscle activation patterns.