Do you think Banquo's "cursed thoughts" are Banquo's own ambitions, his fears about how Macbeth will act on his prophecy, or both? Explain.

I think that Banquo is referring to both his own ambitions
and his fears about Macbeth when he speaks of his "cursed thoughts."  At the beginning
of Act 3, Banquo thinks about the witches' prophecy having come true for Macbeth, and he
wonders whether or not it will come true for him as well, and if so, when?  Yet, at the
same time he also thinks that Macbeth has done evil things to ensure that the prophecy
would come true for him.  Banquo is tormented by these conflicting thoughts because he
feels that gathering up his hopes is unfair, especially if it will lead to evil deeds. 
He banishes these thoughts from his mind as the other characters enter the
scene.