To "accuse" in the Bible represents a sort of spiritual accusation. It’s an attack aimed not at a person, but at the spiritual ideas represented by that person. In general, then, it represents being opposed to doctrinal ideas, actively resisting concepts of the Lord and His wishes.

In Revelation 12:10, "accuse" here also signifies the opposition of the dragonists, i.e. people who are in faith alone, to the doctrine of the New Jerusalem and those who live it. (Apocalypse Revealed 564, Apocalypse Revealed 554)

(Reference: Apocalypse Explained 746, 747)