not enough information...
what microphone?
how is it placed?
have you tried all the standard methods of reducing noise?
-having the microphone on a boom next to your face not on the desk
-adjusting gain after you have the microphone off the desk and near your face
-using a noise gate or similar
-placing the microphone away from ambient noise as best as possible
short answer? use proper placement, do not use too much gain generally