Unhygienic food handling practices lead to most outbreaks of foodborne diseases in the food business. One effective method to keep food safe is through training food handlers. In 2017, Muscat Municipality initiated a certified training program for food managers or supervisors. Since then, no evaluation of the effectiveness of the training program has taken place. This study aimed to evaluate the efficacy of the training program on food safety knowledge, attitudes, and self-reported practices (KAP) of food managers/supervisors in Muscat Governorate. Food safety KAP among 184 food supervisors in food service establishments in Muscat, Sultanate of Oman, was evaluated. The data was collected through a questionnaire consisting of four sections: demographic characteristics, knowledge, attitudes, and practice. The results showed that most food handlers were 31 to 40 years old, 58% had more than a high school education, and 69% were from Southern Asia. In addition, about 46.2% of food supervisors had completed a food safety training course required by Muscat Municipality, attended in 2017, and the language of the course was mainly English. There was a significant (p < 0.05) association between food safety KAP and food managers' education and food safety training enrollment. Supervisors who took training had higher scores mean of knowledge of 102.99 than the untrained 83.49. The mean rank of attitude for trained supervisors was 100.79, and for untrained, it was 85.38. Also, the mean practice rank was higher for trained supervisors than untrained ones, which were 103.72 and 82.86, respectively. In addition, there was a significant correlation between food safety knowledge and food supervisors' work experience. A significant positive correlation was detected between knowledge and attitude (rho = 0.588, p < 0.05), knowledge with practice (rho = 0.417, p < 0.05), and attitude with practice (rho = 0.348, p < 0.05). Although food supervisors' knowledge, attitude, and practice levels were satisfactory, the study suggests that several aspects related to improper handling of food, time and temperature control, and prevention of food poisoning should be emphasized. Training should be mandatory for all food managers and food handlers.