Ward off means to keep something away from you. You're keeping them away.
"I play this sound to ward off bears.
Steer clear of means you avoid the subject.
"I steer clear of bears by not going to the mountains."
Keep away can mean either, based on how it is used.
"This spray keeps away mosquitoes." The spray wards off mosquitoes.
"Keep away from the fence, it is dangerous." You should steer clear of the fence.