In the web view, at the top of the board, you see a list of members. If you select the invited member and then just hit remove, you can remove them from the board.
Trello treats invited members as members of the board who simply have not set up their account yet, so it works the same way as removing any other member.
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.