TextBox.TextChanged event firing twice

 TextBox.TextChanged event firing twice
i am using windows server 2012 r2, i used textboxchanged event which is fires twice for on change click.
the below code execute twince for one click
protected void txtm1_TextChanged(object sender, EventArgs e) {
if (txtm1.Text != "") {
............................................ } else {
........................................................ } 
}