In this paper, the sympathetic and parasympathetic responses are found out to monitor mental stress during playing car racing game. Mental stress is very important issue to address because of its severe consequences. The heart rate variability (HRV) analysis is performed to find these responses. HRV features are derived from the electrocardiogram (ECG) signals of six healthy participants and analyzed in time and frequency domain. HRV features such as mean heart rate; mean normal-to-normal (NN) interval, standard deviation of NN (SDNN) interval, root mean square of successive NN periods (RMSSD), low frequency (LF) components, high frequency (HF) components, ratio of LF/HF (LF/HF), normalized LF(LF(n.u.)) and HF (HF(n.u.)) were derived to monitor mental stress in terms of sympathetic and parasympathetic activity. HRV is helpful to use because it can detect the changes in autonomic nervous system that are well defined to predict mental stress with certainty. © 2012 IEEE.