No. The author's consent to open access for a given article is manifested by self-archiving the article in an open access repository, by publishing it in an open access journal, or by some explicit statement attached to the article. Open access repositories and journals will help readers by making clear that they offer open access to all their contents, and they will respect authors by offering open access only to the works for which their authors have consented to open access. However, if a copyrighted work is on the internet but not in such an archive or journal, and there is no other indication of the copyright holder's wishes, then users should seek permission for any copying that would exceed fair use.
(From the Budapest Open Access Initiative: Frequently Asked Questions)