Evaluation of workplace ergonomics for office workers is significant for occupational health. Since office employees’ work is often mental, this evaluation should include a mental work-load assessment as well as a physical assessment. The purpose of this study is to examine the physical and mental workload of office workers of an automotive supplier company. This study was carried out on 250 office workers. The musculoskeletal and physical risks were investigated using Rapid Office Strain Assessment (ROSA) and Cornell Musculoskeletal Dis-comfort Questionnaire (CMDQ), and the mental workload was analyzed with NASA Task Load Index (NASA-TLX). Musculoskeletal disorder risk and mental workload levels were revealed by statistical analysis and examined on the basis of departments. The correlations between risk levels obtained by different methods and the effect of gender and age factors were also investigated. ROSA final score average was 3.69 which corresponds to a moderate risk level. 62.4% of the employees for the chair section and 64.4% of them for the keyboard and mouse section were at moderate and above risk levels. According to the CMDQ results, the body regions with the most discomfort were determined as the neck, upper back, lower back and right wrist. NASA-TLX scores showed that the highest mental workload occurs in office workers in Accounting, Maintenance and Purchasing departments. NASA-TLX scores were found to be correlated with the ROSA final score, but not with the CMDQ scores. Evaluating the musculoskeletal disorder risks and mental workload of office workers together and taking the necessary precautions were beneficial in terms of protecting the health of the employees.