There have been some studies on the relationship between tension-type headache (TTH) and physical activity. However, most previous studies were not prospective and assessed physical activity by questionnaire. Therefore, this study was aimed to investigate the relationship between TTH intensity and physical activity prospectively utilizing computerized ecological momentary assessment and actigraphy. Thirty-one TTH patients wore watch-type computers equipped with actigraphy inside for 1 week to record momentary headache intensity and physical activity. Multilevel modelling was used to investigate the effect of headache intensity on the simultaneous and subsequent activity level. There were significant negative associations between headache intensity and the simultaneous and subsequent activity level, and activity level was significantly reduced at headache exacerbations. These results provide objective and quantitative evidence suggesting that TTH negatively affects physical activity.