\documentclass[a4paper,12pt]{article}
\usepackage{amsthm,amssymb,amsmath,mathrsfs,amsfonts}
\usepackage{xepersian}
\settextfont[Scale=1.1]{XB Zar}
%\settextfont

\begin{document}  
متن 
$111$
\begin{align*}
a + b_2 = 0
\end{align*}
\end{document}
