At work, people may experience fatigue and a depletion of mental resources. The subsequent need for recovery is generally assessed employing subjective reports on evaluative statements. In this paper, we explore whether it is possible to assess employees’ recovery needs with a systematic inspection of behaviors. The idea is based on Campbell’s paradigm (Kaiser, Byrka, & Hartig, 2010), which holds that individuals will perform more, and more difficult behaviors to recover from fatigue when their need for recovery is higher. We developed a behavior-based questionnaire and tested its reliability and validity in three subsequent survey studies (N = 278, N = 121, and N = 237). Results indicated that the behavior-based Need for Recovery scale (bbNfR) was internally consistent and robust, and converged with the evaluation-based Need for Recovery scale by Van Veldhoven and Broersen (2003). In addition, the bbNfR proved sensitive to different lighting conditions. This suggests that context and ambient conditions can be relevant for the extent of recovery needs and for the mental fatigue people encounter, also in real-life settings. The studies demonstrate that it is possible to measure office employees’ recovery needs with a behavior-based assessment. In addition, the research illustrates how frequently and persistently need for recovery influences office workers’ work and work practice, as they deliberately or inadvertently engage in activities to seek restoration of mental capacity.