Background: Office workers are high-risk populations for their sedentary behavior and its related diseases. This study examined the structured intervention on physical activities in employees. Methods: In this quasi-experimental study, 189 participants were allocated to two experimental and control groups using the multistage random sampling method. Data were collected through the short form of an international physical activity questionnaire, and a structured researcher-made questionnaire containing demographic and questions related to the constructs of the theory of planned behavior (TPB). The experimental group contributed to four training sessions and four practical walking meetings. Data were analyzed by SPSS software (version 19) using independent t test, chi-square, and linear regression tests at the significance level of 0.05. Results: There was no significant difference between the two groups before the intervention regarding the mean score of attitude, subjective norms, perceived behavioral control, behavioral intention, physical activity, and demographic variables (P>0.05). After the intervention, the mean score of attitude, subjective norms, perceived behavior control, behavioral intention, and physical activity in the experimental group was significantly higher than the control group (P<0.05). Conclusion: The finding of this study suggests that TPB is a suitable framework for designing physical activity interventions among office workers.