Mental workload is a popular topic for ergonomics, psychology, and organizational behavior-related studies. Difficulties and differences in defining and measurement of mental workload engage the attention of scholars to the concept. Furthermore, the importance of mental workload on performance and burn out increases attention to the topic for empirical studies. In this chapter, the authors reveal the relations between mental workload, burnout, and job performance. Data were obtained from 144 academicians in Turkey. Results demonstrated that mental workload has a 1) positive impact on burn out and 2) negative impact on job performance of academicians. Moreover, it was found that burn out and job performance are negatively correlated. Finally, findings reported that there are differences among some demographic variables in accordance with mental workload, burn out, and job performance.