Purpose: This study aimed to evaluate the effects of an ergonomic dentist stool design on muscle activity and fatigue in dentists. Materials and methods: Fourteen dentists were recruited, and electrodes were attached to the arm, neck, and shoulder muscles of these dentists according to the Surface ElectroMyoGraphy for the Non-Invasive Assessment of Muscles protocol. After measuring the maximal voluntary contraction, eight-channel surface electromyography was performed during simulations of two dental procedures (intraoral scanning and tooth preparation) while the dentists were using two types of dentist stools. Furthermore, muscle activity and fatigue were determined based on the eight-channel surface electromyography data, and ergonomic risk levels were evaluated according to the muscle activity. The Shapiro–Wilk test was used to confirm that all data were normally distributed, and the Mann–Whitney U test was used to compare the two types of dentist stools (α = 0.05). Results: There was a significant difference between the conventional and ergonomically designed dentist stools in terms of the activity of trapezius descendens muscle (p < 0.05). Notably, the activity of the trapezius descendens muscle was lesser when the dentists used ergonomically designed dentist stools than when they used a conventional dentist stool. The activity of all muscles, except for the sternocleidomastoid, indicated moderate ergonomic risk. Conclusion: A dentist stool that enables dentists to maintain ergonomic posture should be used to prevent musculoskeletal disorders.