Alert message on button click event

I have a button and textbox on my page aspx and on button click event I am displaying alert message.

Now when I run website and click on button it display message but after that when I press F5 (Refresh) it again display message. So my question how to remove message when I click F5.

Below is my code for button click:

  protected void btnExport_Click(object sender, EventArgs e)
  {
      DisplayMessage("There is no data to Export.", this);
        
  }
  
       

and

public void DisplayMessage(String strMessage, Control name)
{
    string script = "<script language='javascript'>alert('" + strMessage + "');</script>";
    ScriptManager.RegisterStartupScript(name, name.GetType(), "JSCR", script, false);
}

Answer

Change your script as follows

string script = "alert('hello');window.location.href='Default.aspx'";

where i assumed Default.aspx is your page