The iphone's SAR rating is well below the critical value determined by the regulating authorities.so it's safe.but no phone has 0 SAR (Specific Absoption Rate) value so some radiation even though it's very little is always there.
So try not to keep ur phone just beside ur pillow when ur asleep.u can keep it beside u but not too close to ur head.
Turn your iphone off ( hold power button, and slide to power it off ) if you don't rely on your phone for wake up calls. There is very little chance of radiation actually harming your brain ( my clueless guess ) or none at all
There is slight radiation that comes from all mobile phones but it is relativity harmless. I would suggest that if your so worried about it then you should just put it on a bedside table or on the floor.