It would mainly depend upon the fact, if the keyword is a generic or a disctinctive word. A generic word will always be safe, provided there is no violation of the rights of .com or any Trademark holder otherwise.
While in case of distinctive words, assumption can be drawn as to knowledge of the mark. In many cases a simple google search can reveal existence of the Trademark holder, so bad faith can be assumed against a domain registrant in case of distinctive marks.