\documentclass{book}
\usepackage{xcolor, empheq}
\usepackage{xepersian}

\begin{document}

\baselineskip=7mm

\begin{empheq}[box=\colorbox{yellow}]{align}
a&=b\nonumber\\
 &=mc^2 + \int_a^a x d x + \int_a^a x d x + \int_a^a x d x + \sum mc^2 + \sum mc^2 + \sum mcg
\end{empheq}

\begin{align}
a&=b\nonumber\\
 &=mc^2 + \int_a^a x d x + \int_a^a x d x + \int_a^a x d x + \sum mc^2 + \sum mc^2 + \sum mcg
\end{align}

\end{document}