Answer:
well, you cant ignore them cuz that wouldn't be nice. Has you best friend told you that they like u? If not, and you just feel like he/she (which ever gender ur best friend is) likes you this is what to do: Try to get them to not like like you. Start talking to them about other hot guys/girls or tell them what is your type (opposite of them). Maybe he/she might give up on liking you.
If this does not work then try being disgusting, do stuff that he/she hates, but don't go to the extreme or else they might never talk to you again. (We don't want that)
If this does not work i think its time to tell the truth. Talk with your best friend and tell them that you don't feel the same way or you don't like them they way they like you. If your scared to do this then let your other friends tell them or something. Make sure say it in a nice way and try not to hurt their feelings.
Good Luck