Napoleon and Macbeth are both tyrannical, power-hungry leaders. Both of them create the main conflict in their respective stories: overthrowing a despot. The difference is that Napoleon replaced a despot with a despot, and Macbeth replaced a worthy king. Napoleon is not successfully overthrown, but Macbeth is.
They are selfish and abusive of their power. Both are most interested in holding on to their power. Napoleon is more interested in the benefits of power than Macbeth.
Napoleon and Macbeth both take out the former leader to get power, but Napoleon does so with a coalition.
After a moment, however, Snowball and Napoleon butted the door open with their shoulders and the animals entered in single file, walking with the utmost care for fear of disturbing anything. (Animal Farm, ch 2)
Macbeth had a partner, Lady Macbeth, but not a coalition. Napoleon prefers to let others do the dirty work, whereas Macbeth kills Duncan himself.
Will all great Neptune's ocean wash this blood
Clean from my hand? (Macbeth, Act 2, Scene 3, p. 31)
Napoleon allows the revolution to proceed, but then he has dogs to do the killing for him, just as Macbeth hires murders.
At the end of Animal Farm, Napoleon remains in power and it indicates that the tyrannical pigs will continue to reign.
The creatures outside looked from pig to man, and from man to pig, and from pig to man again; but already it was impossible to say which was which. (Animal Farm, ch 2)
Like Napoleon, Macbeth is a terrible leader. He kills everyone who disagrees with him. Yet while Napoleon did not have opposition, Malcolm is able to raise an army against Macbeth and Macduff kills him.
Behold where stands
The usurper's cursed head. The time is free. (Macbeth, Act 5, Scene 8, p. 90)
So while the conflict that Macbeth causes ends with his death, Napoleon’s continues on.