Final answer:
Lady Macbeth dismisses the lords from the feast when Macbeth sees Banquo's ghost.
Step-by-step explanation:
The person who dismisses the lords from the feast when Macbeth sees Banquo's ghost in Macbeth is Lady Macbeth.
In Act 3, Scene 4, after Macbeth is tormented by the ghost of Banquo, Lady Macbeth intervenes and dismisses the lords, attempting to cover up Macbeth's strange behavior. She claims that Macbeth has been plagued by these fits since his childhood and urges the guests to leave the banquet.