Estimating a driver’s mental workload level is challenging part nowadays. In this study, an experimental investigation was conducted to explore mental workload using blood-volume-pressure (BVP) and electrocardiogram (ECG) signals. Participants performed two secondary tasks at two levels of task difficulty and also in two types of traffic conditions. The results show that increasing task difficulty seems to increase heart rate (HR) and reduce the heart rate variability (HRV) data simultaneously. Especially, data for HR was high when the drivers were performing the most difficult task for the mathematical arithmetic task. Results from BVP and ECG also show that they correlate each other showing that BVP can be used as a potential candidate as a mental workload measurement tools. Potential applications of this research include developing a method to estimate a driver`s mental workload level through blood volume pressure as the main measurement for evaluation of mental workload as it is non-intrusive to drivers.