There is a change in the behaviour of Macbeth from the early Acts (I, II), and the turning point for Macbeth is the manifestation of the ghost of Banquo, a figment (possibly) of his guilty conscience. This will be the last time that Macbeth suffers a pang of guilt or any awareness that his actions are evil. From his first appearance in Act IV to the end of the play, his only concern in the play is to hold onto the kingship, whatever and whomever might get in his way. So, it is in the early Acts of the play that we must look for this awareness of good and evil in his thoughts and actions.
In these opening Acts, the biggest sign of his awareness that the temptation to kill Duncan and fulfill the witches prophecy so that he can become king is an evil one comes in his soliloquies. These conversations with the audience, that take place when he is alone onstage, come in Act I, scene vii; Act II, scene i; and Act III, scene i. All of these speeches reveal Macbeth's concern that what he does will, as he admits in Act I, scene vii:
commend the ingredients of [his] poison'd chalice
To [his] own lips.
This line reveals an awareness that the evil concoctions he creates for others will also be the agent of his own demise. And, in each speech, he must fight with himself a bit to overcome his better nature.
In Act II, scene i, he confesses to having a "heat-oppressed brain," or mental anguish, about the dagger that he must take up to commit the murder. The appearance of the apparition of a dagger only reminds him to get himself back on track and do what must be done, even if it is wrong -- murder.
And in Act III, scene i, he plots to murder Banquo and his son Fleance so that the prophesy that Banquo's issue will be kings won't be fulfilled, but also because Macbeth's
. . . fears in Banquo
Stick deep. And in his royalty of nature
Reigns that which would be fear'd. . .
. . .There is none but he
Whose being [Macbeth does] fear. And under him
[Macbeth's] Genius is rebuked.
Macbeth admits here that Banquo is a better man than him, and this is a clear recognition of his own evil. Macbeth now lists his own evil nature as a justification for killing Banquo, an act he must commit so that Banquo's light of goodness will not outshine Macbeth's evil one.
For more on these speeches and how they reveal Macbeth's self-awareness, please follow the links below.