Set focus on alert message ok button

Set focus on alert message ok button

Hi,

I am using the below code to show the alert message 

             string lstrScriptMsg = "alert('" + astrErrorMsg + "');";
            ScriptManager.RegisterStartupScript(this, GetType(), "Alert", lstrScriptMsg, true);

During my Page flow I used to show this alert message whenever PDF files are generated.But the actual Problem is This alert message getting displayed behind the PDF file.So I thought of making the alert message box should be the Top of the Current window.

So can We get focus on alert message box ok button? or any other better suggestions on this?