Free-flying honeybees can electrostatically collect particles from air in the flying and foraging areas, which in conjunction with organic-based explosive vapor sensing films, placed at the entrance to the beehive, can be used as a passive explosive sensing mechanism. Moreover, bees can be trained to actively search for a smell of explosive. Using trained honeybees in conjunction with a system for honeybee localization enables generation of a spatial-time honeybee density map, where the most visited places point to suspicious areas. In both methods (passive and active), bees' activity monitoring plays a significant role, providing information about environmental parameters and activities of bees at the entrance and exit of a beehive. In this paper we present the design and realization of an electronic system for bee activity monitoring at the front of a hive while using bees for explosive detection. The system also monitors air temperature and relative humidity. Results obtained to date from activity monitoring are useful in planning testing activities within our active and passive method, as it can determine the optimal period of the day and environmental parameters in which bees are most active.