Protein moves out from PBC

Hi

I run the simulations using the CHARMm 22 force field in Discovery Studio 2.1. after 1 ns simulations, I observed the protein flows out (moved from the center of box)from the PBC box but the simulations seems to be successful. Is there any problem in my simulations or can I continue my further simulations?. I would like to know why the protein tries to go out from PBC?

Do I need to change the forcefield or any parameter in simulation protocol?

Please help me

Thanks so much in advance