You have to manually add the "Bibliography" entry into the table of contents. In order to do so, put the following just before the \bibliography entry

\addcontentsline{toc}{chapter}{Bibliography}

if you use the book or report document class, or

\addcontentsline{toc}{section}{Bibliography}

if you use the article document class.

In combination with the "Hyperref"-Package you need to put the line below the \bibliography entry.