The concept of human mental workload in the field of human factors and psychology has a long history with important applications in the aviation and automotive industries. The main objectives of this literature review are defined the ‘mental workload’ term and determined mental workload measurement methods in driving task. Mental Workload is a complex concept and it is difficult to define this term. It has no a universal accepted definition. Mental workload level cannot be detected directly, however, it has found that relates to limitation of individual internal resources to accomplish the task, and also involves a multi-dimensional variable. Previously, several studies have been indicated that mental workload relate with operators’ performance, task demand and mental resource supply. Extremes (underload or overload) mental workload can degrade operators’ performance. Several assessment methods have been proposed for investigating mental workload. They can be performed in experimental or operational settings. There are seven selection criteria to select the most appropriate methods. These include sensitivity, diagnosticity, intrusiveness, implementation requirement, operator acceptance, selectivity and bandwidth and reliability. Dozens of Mental workload measurement techniques have been developed and categorized into three main groups. (i) Subjective rating, which were categorized into unidimensional and multidimensional. NASA-TLX, SWAT, RSME and MCH are the famous examples of subjective-based techniques. (ii) Performance measures are divided into primary task and secondary task measures. Primary task measures are capable of discriminating the resource competition between individual differences. For example, speed instability, distance headway instability, lateral position from road centerline, lane excursion, time spent out of lane can be widely used to represent the driver primary performances. In secondary task measures are more diagnosticity than primary task measures and subjective measures. Correct response, time response of additional secondary task are a well-known examples of secondary task performance measures in driving research. Additionally, (iii) Physiological techniques also have high sensitivity in measurement, but results from these methods can easily are confounded by other external and extraneous interference. Measures of Eye Functions have been frequently used if compared with other Physiological techniques. It can be argued that the combined methods are recommend cooperatively to predict human mental workload.