Main Level "running alive" while i'm inside other levels

Hello members, i’m in a game design where basically there is a main MAP(MaimLevel) of type TopDown with your Char and others NPCs AI and some places like caves, cities, empty areas where you can enter and other MAP(level) is loaded and now you are in a Third person game mode exploring the area. Well, while you are in this new map, can my MaimLevel(the TopDown) be running alive with the AI doing there jobs? Like 2 levels running at same time, after i left the new area and unload it i back to the Mainlevel(topDown) and every thing will be diferent before i got into the new area. I’ll i got so far is using the savegame for the storage my MainMap to load back after i left the new areas.