Several types of conflict are present in the first act. Initially, we notice that Macbeth is involved in a war between his own Scotland and Norway. In addition, a traitor from within has threatened Scotland's safety.
More importantly, the chief internal conflict occurs within Macbeth. Once he hears the witches prophecies, he is torn as to whether he should succumb to the "horrid image" that "unfixes" his hair - killing the King to hurry along the prophecy.
This conflict spreads to his wife when she learns of the witches prophecies and the King's imminent arrival. She harangues Macbeth incessantly until he agrees to do the deed. If the conflict was internal, it is now external and will soon become everybody's problem.