\documentclass[a4paper,12pt]{book}

\usepackage{xepersian}


\settextfont[Scale=1]{Yas}
\setlatintextfont[Scale=1]{Yas}

\begin{document}

\bibliographystyle{unsrt}
\resetlatinfont
\begin{thebibliography}{99}

\begin{LTRitems}
\bibitem{b1} aaaa 
\end{LTRitems}
\end{thebibliography}
\end{document}