\documentclass{standalone}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\draw[thin,->](-.5,0)--(5,0);
\draw[thin,->](0,-.5)--(0,2.5);
\draw[very thick] (0,0)--(4,0) arc (0:30:4)--(0,0);
\node at (.15,-.2) {$O$};
\node at (4,-.2) {$A$};
\node at (3.5,2.2) {$B$};

\end{tikzpicture}

\end{document}