An empirical study was conducted to find out the level of propensity to serve in the Active Reserve of the Serbian armed forces and Ministry of Defence according to a newly established concept of manning. The concept of Active Reserve corresponds to similar concepts in other countries and is of growing importance and actuality, particularly in countries which have recently abandoned their military conscription system aiming to create professional military forces that citizens can join voluntarily. The concept of Active Reserve assumes that a citizen signs a contract with the Ministry of Defence, confirming his or her willingness and readiness to serve in the military on call, while in the meantime living and working on their own. Active Reserve offers mutual benefits: it relaxes temporary problems related to manning of military units and is a source of additional money for individuals engaged in it. One of the main questions related to the Active Reserve is the level of propensity to serve in it, while equally interesting is the investigation of motivational factors which stand behind the willingness to serve. The results show a very high propensity of population to serve in the country and a significant level of readiness to participate in peace missions abroad. The structure of motivational factors to join the Active Reserve indicated a meaningful level of a security awareness of the population. These findings are in concordance with some novel results about security perceptions in the South-Eastern Europe, including Serbia.