Background: The aim of this study was to examine whether a low-cost standing desk intervention that reduced occupational sitting was associated with changes in work-time cognitive–affective states in real time using ecological momentary assessments at the start and end of the trial. Methods: Forty-one office employees (91.7% female, mean age = 39.8 [10.1] y) were randomized to receive a low-cost standing desk or a waitlist control. Participants received 5 surveys each day for 5 workdays via smartphone application prior to randomization and at trial’s end. Ecological momentary assessment assessed current work-time psychological states (valence and arousal, stress, fatigue, and perceived productivity). Multilevel models assessed whether changes in work-time outcomes over the course of the intervention were significantly different between treatment groups. Results: There were no significant differences in outcomes between the groups except for fatigue, with the control group reporting a significant decrease in daily fatigue following the intervention (P < .001). The intervention group reported no significant changes in any of the work-time outcomes across the study period (P > .05). Conclusions: A low-cost standing desk intervention to reduce occupational sedentary behavior did not negatively impact work-time outcomes such as productivity and fatigue in the short term.