Depends. Under OBR rules, the determination is supposed to be made by the umpire as to whether he demonstrated an attempt to steal. For example, simply feinting in a way as to make the pitcher reasonably think he was trying to steal is enough to keep it from being a balk. Before the comment, umpires used to have a variety of ideas on the subject - everything from had to actually be going to going half way, etc.
Rule 8.05(d): The pitcher, while touching his plate, throws, or feints a throw to an unoccupied base, except for the purpose of making a play
Rule 8.05(d) Comment: When determining whether the pitcher throws or feints a throw to an
unoccupied base for the purpose of making a play, the umpire should consider whether a runner on the previous base demonstrates or otherwise creates an impression of his intent to advance to such unoccupied base.