Leaving any kind of powder in an enclosed place where it can be subjected to some extreme temperatures, especially heat is not a good idea. I believe there is even a warning on the powder jug to that effect. While I am not saying it will explode, there always is the possibility, so for safety reasons I would not do it...

If you have shot your rifle and will not be shooting it for an extended period of time, then by all means clean the rifle. Some powders like Pyrodex RS for instance can start rusting the bore in a matter of days. If the rifle was subjected to moisture on top of that, it can accelerate the process.