Objectives : This study was performed to investigate the effect of acupuncture at Yintang point(EX-$HN_3$) on heart rate variability in healthy adults with mental stress. Methods : 38 healthy volunteers(sham point group : 19, Yintang point group 19) participated in this study. The study was established by randomized trial. After 10 minutes rest period, mental stress was provided for 10 minutes. HRV was recorded before and after stress. And then simple acupuncture was applied at sham or Yintang point for 15 minutes. We measured HRV 3 times: before and after stress, and after acupuncture. Results : In sham point group, LF norm and HF norm changed significantly after mental stress. In Yintang point group, LF, HF, LF norm, HF norm and LF/HF showed a significant change after mental stress. In sham point group, all indicators were not affected after acupuncture. In Yintang point group, HF norm decreased significantly. LF, LF norm and LF/HF increased significantly. There were significant differences between two groups(p<0.05). Conclusions : The results suggest that acupuncture at Yintang point(EX-$HN_3$) can regulate and prevent the alteration of autonomic nerve system by mental stress.