Background: We aimed to find the commonly used assessments to evaluate driver's mental workload and its relationship with driving distraction. Methods: Academic articles such as journals, books, reports and conference papers that are related to workload measurements methods used in identifying mental workload among drivers that are dated from Jan 2015 to Apr 2020 were used in this paper. Then, PRISMA checklist and flow diagram are being applied. Results: The few commonly used assessments in evaluating mental workload among drivers are Karolinska Sleepiness Scale (KSS), NASA TLX, Electroencephalogram (EEG), Heart Rate (HR), eye tracking and driving performance. Moreover, different types of driving distractions show to affect the driver's mental workload in one way or another when being evaluated using these assessments. Conclusion: The finding of this study can be used to find the gap for future research in vehicle safety by using multimodal monitoring of different types of assessments to increase the validity and robustness in driving assessment.