When we refer to mood we are thinking of the overall emotion produced by a work of literature. The mood of a text can normally be described by one or two adjectives, such as "bittersweet" or "comic," and so it is important to read the text you are studying and try to work out what mood the author is trying to create.
In the ninth stanza of "The Raven," it appears that the predominant mood is one of confused wonder. The stanza begins by the speaker reporting how he "marvelled" at the raven and the way that it could pronounce the word "Nevermore" so plainly. He muses on the fact that no other human will have had the same experience of a raven sitting on the bust above his chamber door with the name of "Nevermore":
For we cannot help agreeing that no living human being
Ever yet was blessed with seeing bird above his chamber door--
Thus it is that the mood of this stanza alone seems to be one of wonder and confusion as the speaker tries to work out what this strange apparition and its speech might mean for him.