Is it.okay to brush after filling?

Yes: Unless your dentist advised otherwise. Amalgam fillings are set enough in approximately one hour. Composite fillings are set enough by the time you leave the office. With temporary fillings you can usually eat and brush also after 30 minutes but will have to be careful with them until replaced with something permanent. I'm not sure which type you are referring to.

Brush and floss: Once numbness is gone, resume your normal brushing and flossing routine. Take care.