I think there is a way in which either is possible, especially based on this particular interaction: I assume you refer to the one among the Weird Sisters, Macbeth, and Banquo in Act 1, scene 3. Several details conspire to characterize the sisters as evil, and, in the first scene of the play, we saw them plan to meet Macbeth on the heath. They indicated that "Fair is foul, and foul is fair," a line which seems to suggest that they will say and do things that appear to be good when they are, in fact, bad (1.1.13). Thus, when they approach Macbeth to tell him that he will become not only the Thane of Cawdor, but also king, we ought to be alarmed when Banquo asks his friend,

Good sir, why do you start and seem to fear
Things that do sound so fair? (1.3.54-55)

These statements sound "fair" or good, but we've already learned that the sisters are not exactly benevolent creatures (one plans to torture a man simply because his wife refused to share her chestnuts!). Therefore, it seems that evil has sought out Macbeth.

On the other hand, Macbeth's response to this interaction makes it seem as though evil is something people choose. After he learns from the Thane of Ross that he has been named the Thane of Cawdor, Macbeth begins to experience a great deal of internal conflict. He says to himself,

I am Thane of Cawdor.
If good, why do I yield to that suggestion
Whose horrid image doth unfix my hair
And make my seated heart knock at my ribs
Against the use of nature? Present fears
Are less than horrible imaginings.
My thought, whose murder yet is but fantastical,
Shakes so my single state of man
That function is smothered in surmise,
And nothing is but what is not. (1.3.146-155)

He cannot decide if this news is good or bad; he has become Cawdor — how will he become king? He begins to consider what might be necessary for this part of the witches' predictions to come true, and he is horrified by what he imagines. In other words, he seems to already be considering performing some terrible actions in order to gain the power he was promised. This suggests that he has a choice: he can do nothing to become king and see what happens, or he can do something nefarious. He will, obviously, choose the latter.