That depends on a number of factors - if you look at your reservation breakdown it shows you what fee you have paid to AirBnB. That bit is non-refunable except under extenuating circumstances.
If it's a general question and you have not booked as yet, then proceed with your booking and on the final page, before you pay, you will see the breakdown and the AirBnB service fee, which can be anywhere between 6-13%.