Jane Eyre is a more complex novel than many, and as such doesn't have a true antagonist. The story is set in several parts. At times, characters act as antagonists, while at other times, the main obstacle to overcome is simply the situation in which individuals find themselves.
In the first portion of the book, Jane's aunt Mrs. Reed and her family are all antagonistic, forcing Jane to do household labor and punishing her by locking her in the room where her uncle died. Later on, at Lowood school, the superintendent, Mr. Brocklehurst, and the majority of the other instructors act as antagonists, tormenting the girls and subjecting them to beatings and harsh conditions, although there are several caring individuals.
Throughout the remainder of the novel, there isn't a true antagonist; however, there is a competitor for Mr. Rochester's affections, Blanche Ingram. Jane eventually reveals her feelings for Mr. Rochester and he reciprocates. Mr. Rochester's first wife acts as a situational antagonist at times, as she prevents Jane and Mr. Rochester from coming together when Jane first learns of her existence, and her insanity leads her to become physically violent with members of the household.
The main obstacle in the novel, however, is simply Jane's inability to be with Mr. Rochester, at least, until the end. They encounter several obstacles, such as Blanche, the first Mrs. Rochester, and the deadly fire, but they are eventually able to be together.