Prolonged sedentary behavior has been shown to increase chronic diseases. Using standing and treadmill desk reduces sitting time, increases metabolic rate and thus has potential to improve health. There is little existing guidance on how to keep thermal comfort when using standing and treadmill desk. It is unknown what are the suitable ambient temperatures for occupants at elevated office activity levels. This experiment investigated thermal sensation and preferred temperature at elevated office activity levels, including sitting (SED), standing (STD), and two slow-walk speeds: walking at 1.2 km/h (TRD1) and walking at 2.4 km/h (TRD2). Comfort votes were obtained from 20 subjects under personal controlled ambient temperature. The active workstation significantly increased human metabolic level and reduced preferred temperature. The measured metabolic rates were 1.0, 1.1, 1.9 and 2.5 met for SED, STD, TRD 1 and TRD 2. The preferred ambient temperature reduced from 25.85 °C for SED, to 25.0, 24.1 and 23.2 °C for STD, TRD 1 and TRD 2 respectively. All subjects were comfortable at their preferred temperatures. PMV model was found to predict too cool temperature than needed for higher metabolic rates.