Actually, I want to supplenment MaxGraves's answer! (but I don't have enough reputation, sorry about that!)
My result will put the "page/total page" rightside and inside the navigation bar, instead of outside.
Note: \addtobeamertemplate{⟨element name⟩}{⟨pre-text⟩}{⟨post-text⟩}, hence you have to notice which bracket you put "page/total page" in. In my case, using Frankfurt theme, which have default navigation bar, put the followings before \begin{document} will show my results as the bottom.
\addtobeamertemplate{navigation symbols}{}{ \hspace{1em} \usebeamerfont{footline}%
\insertframenumber / \inserttotalframenumber }
The reason I use \hspace{1em} \usebeamerfont{footline} is for good-looking, the front makes "page/total page" not too close to navigation bar, and the latter is just make it as big as I hope, more clearly, I think....

\setbeamertemplate{navigation symbols}{% \insertslidenavigationsymbol \insertframenavigationsymbol \insertsubsectionnavigationsymbol \insertsectionnavigationsymbol \insertdocnavigationsymbol \insertbackfindforwardnavigationsymbol \hspace{1em}% \usebeamerfont{footline} \insertframenumber/\inserttotalframenumber% }– Anderson Oct 08 '13 at 20:43\addtobeamertemplateinstead of\setbeamertemplateyou keep the symbols – Bordaigorl Oct 08 '13 at 21:49\raisebox{1.2pt}[0pt][0pt]{\insertframenumber/\inserttotalframenumber}. – Steve Oct 11 '17 at 18:46