Background: Protected areas are important attractions for promoting healthy life habits. Consequently, to date, a number of studies have examined the association between visitors’ characteristics and physical activities. However, little is known about the specific users inclined exclusively to have sedentary behavior during a visit. Thus, using the Alt Pirineu Natural Park (Spain) as a case study, the aim of this study is to determine the influence of sociodemographic, trip, motivational, and opinion descriptors on the likelihood of participating in sedentary behavior while visiting a protected natural area. Methods: The data used were randomly collected from visitors through an onsite structured questionnaire (N = 628). Results: Metabolic equivalent consumption was used to empirically distinguish the sedentary (22.6%) from the active (77.4%) visitor groups. A logistic regression analysis indicated that the trip and motivational descriptors explained the highest degree of the overall variation in reporting sedentary behavior. Conclusion: The study contributed to documenting the information about visitors’ behavior in protected areas, and the findings may aid park managers in developing effective management strategies for promoting and enhancing physical activity in protected natural areas.