Objectives : The purpose of this study was to assess the effect of $PC_6$ moxibustion treatment for reducing mental stress using power spectrum analysis of the heart rate variability(HRV). Methods : 20 healthy volunteers(simple rest group : 10, moxibustion treatment group : 10) participated in this study. After instrumentation and 5-minutes rest period, mental stress by operation was provided for 5-minutes. HRV was recorded before and after the mental stress. And then the simple rest group rested for 15-minutes. The moxibustion treatment group was treated by $PC_6$ moxibustion and rested for 15-minutes. And then HRV was recorded. Results : In simple rest group, LF norm and HF norm showed a significant change after mental stress. In moxibustion treatment group, LF, HF, LF norm, HF norm and LF/HF showed a significant change after mental stress. But there were no significant difference between two groups(p>0.05) except HF. In moxibustion treatment group, LF, LF norm, HF norm and LF/HF showed a significant change after moxibustion treatment. There were significant differences between two groups(p<0.05). Conclusions : The result suggests that $PC_6$ moxibustion treatment can regulate and prevent the alteration of autonomic nerve system by mental stress.