You can use TeX4ht. It can output math as mathml which can be then displayed with mathjax. You can also configure html header to load mathjax script from mathjax's cdn:
\Preamble{xhtml,mathml}
\Configure{VERSION}{}
\Configure{DOCTYPE}{\HCode{<!DOCTYPE html>\Hnewline}}
\Configure{HTML}{\HCode{<html>\Hnewline}}{\HCode{\Hnewline</html>}}
\Configure{@HEAD}{}
\Configure{@HEAD}{\HCode{<meta charset="UTF-8" />\Hnewline}}
\Configure{@HEAD}{\HCode{<meta name="generator" content="TeX4ht
(http://www.cse.ohio-state.edu/\string~gurari/TeX4ht/)" />\Hnewline}}
\Configure{@HEAD}{\HCode{<link
rel="stylesheet" type="text/css"
href="\expandafter\csname aa:CssFile\endcsname" />\Hnewline}}
\Configure{@HEAD}{\HCode{<script type="text/javascript"\Hnewline
src="http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML"\Hnewline
></script>\Hnewline}}
\Configure{@HEAD}{\HCode{<style type="text/css">\Hnewline
.MathJax_MathML {text-indent: 0;}\Hnewline
</style>\Hnewline}}
\begin{document}
\EndPreamble
With this config file, we request to output math as mathml, then configure html header so resulting file is html5. Save it as for example ht5mjlatex.cfg and then call from command line:
htlatex filename.tex "ht5mjlatex.cfg, charset=utf-8" " -cunihtf -utf8"
or you can use William F. Hammond's script (at bottom of the page)