In the beginning of act one scene two, Macbeth and Banquo meet the Weird Sisters shortly after their victory over Macdonwald and the Norwegians. The witches address Macbeth as Thane of Glamis and Inverness, as well as their king, while they claim that Banquo would father many kings. Macbeth then questions the nature of the prophecy, and wonders
“if good, why [does he] yield to that suggestion/Whose horrid image doth unfix [his] hair/And make [his] seated heart knock at [his] ribs/Against the use of the nature? Present fears/Are less than horrible imaginings./[His] thought, whose murder is yet but fantastical,/That function is smothered in surmise,/And nothing is but what is not,” (I.iii, 147-155).
This indicates that Macbeth has thought of becoming king, but that he may have to act upon the throne at the earliest