Does Macbeth seem interested in being king in Act One, even though his friend Duncan currently holds that title?
Macbeth is intrigued, if very confused, by the prophecy of the witches. As they vanish, he beseeches them to explain themselves further. When Angus arrives, and informs him that he is, indeed, to become the Thane of Cawdor as the witches predicted, he says in an aside:
Glamis, and Thane of Cawdor!
The greatest is behind.
While Banquo warns him to ignore the witches' prophecy, he cannot shake the idea that he is to become king. He remains disturbed, however, by the prophecy, which he says is a suggestion "whose horrid image makes my hair stand on end."
By the end, however, he seems reconciled to what may be his fate, though he does not seem quite aware of what may be required to bring him to that point:
If chance will have me king, why, chance(155)
may crown me Without my stir.
We do not see signs of the ambition that will characterize Macbeth later in the play, but he is certainly thinking deeply about his future, and accepts the idea that he might be king, whatever implications that may have for his friends.