The old series would never really clear an area.
You could kill whatever you found in one spot, then walk around for some time and come back to that same spot to find new enemies.
Is that true for BT IV as well or can I actually clear a level/an area and roam around freely afterwards without facing any more enemies?

Yeah, there are no random encounters, you see the enemies. Certain plot events will spawn or despawn enemies, but for the most part, once you've killed a group of enemies, you can walk around the area freely. You can also usually avoid fights since most enemies path around a bit, if you so desire.