Objective: Insufficient physical activity (PA) is a well-known risk factor for many non-communicable diseases. This study aimed to develop a screening tool to identify physically inactive people at the population level and to help social and health care professionals promote physical activity among people at risk. Methods: Eighty-five healthy adults wore a hip-worn accelerometer for seven days, after which they completed several PA questionnaires. These included some novel and several validated questions on PA. The reliability of individual questions to identify physically inactive people was assessed by correlation analysis. Logistic regression analysis was used to find the combination of questions which best identified physically inactive people. Results: The highest correlation of the screening questionnaire with the accelerometer was 0.46 (p < 0.001) for sedentary behavior and 0.42 (p < 0.001) for total physical activity, respectively. The best pair of questions on total physical activity identified 64% of all inactive subjects (MVPA < 150 min/week) based on accelerometer data. Conclusions: The questionnaires developed for screening PA have a poor correlation with the accelerometer data. The screening questionnaires roughly describe PA level among middle-aged participants, but if a more sensitive or specific method is needed, device-based measurements are recommended.