I recently watched the movie "The Sixth Sense". It seems that Cole is not afraid of Dr. Malcolm Crowe compared to other ghosts that he also sees in the movie. Is there a plot hole or is there any explanation for it?
As Steve-O states in his comment Cole was somewhat nervous or even afraid of Malcolm during their initial meetings. A viewer unaware of the "twist" of the film would likely assume that it is just the normal wariness a child would have around a new therapist and not put too much weight on it. In all likelihood had he not shown those sorts of nerves that would have been more obvious to the audience.
As they spend more time together Cole grows to trust that Malcolm isn't the sort of ghost he needs to be afraid of and his growing comfort at being around Malcolm mirrors his arc towards coming to accept the other ghosts and help them instead of being afraid of him. Add in that Malcolm's appearance and manner is nowhere near as frightening as some of the other ghosts we encounter that Cole sees and it's understandable that he wouldn't feel as scared by him.