Introduction: Caffeine is a naturally occurring substance that is widely consumed in a variety of forms. The aim of this study was to assess the effect of caffeine on blood pressure in overweight men during exercise and at rest. Materials and Methods: In double-blind randomly designed study, six men (BMI 29.55±1.22 kg/m2, age 22.50±0.83 yr, height 174±9.12cm, weight 89.31±8.85kg, body fat percent 26.38±3.62) with sedentary lifestyles, performed 30 minutes running on treadmill at similar exercise intensities (60% VO2max), 1 hour after taking caffeine (5 mg/kg body weight) or placebo. Heart rate was recorded during exercise, and blood pressure (BP) was measured before and 1 hour after taking caffeine and immediately after exercise, and data analysis was conducted using student' t-test. Result: Results indicated that systolic and diastolic BP and mean arterial pressure significantly elevated following caffeine intake at rest, but no significant differences were observed after exercise no significant differences were observed between caffeine and placebo in heart rate during exercise. Conclusion: The findings indicate that caffeine at this dosage level alters cardiovascular dynamics by augmenting arterial blood pressure in moderately obese men at rest. However, it seems that taking caffeine before exercise does not cause abnormal elvations in blood pressure in moderately obese men.