Of course, Macbeth is intrigued by the prophecy that he will be Thane of Cawdor and king. Banquo notes this, saying to the witches that Macbeth "seems rapt withal" (I.iii.55). In other words, Banquo notices how Macbeth seems enchanted with their predictions. The witches also predict royalty in Banquo's descendants. The third witch says, "Thou shalt get kings, though thou be none" (I.iii.65). Banquo is equally intrigued by this but he is much more skeptical than Macbeth. Banquo tells Macbeth to be wary.
And oftentimes to win us to our harm
The instruments of darkness tell us truths,
Win us with honest trifles to betray's
In deepest consequence. (I.iii.121-124).
Here, "betray's" means to "betray us." A bit further down, Banquo comments to Ross and Angus how Macbeth seems to be enchanted (he uses the word "rapt" meaning enraptured) with these notions. Banquo is skeptical from the start, noting how the witches look like women with beards, unnatural in his eyes. He is even more skeptical with their royal prophecies for his kin and Macbeth. Finally, Banquo is also concerned with how quickly Macbeth is taken in by the prophecies.