Hey Madhuri,
Use below code,
.cs Code:
TextBox txt = new TextBox();
txt.ID = "txt_name";
Panel1.Controls.Add(txt);
MaskedEditExtender mee = new MaskedEditExtender();
mee.Mask = "999-999-9999";
mee.MaskType = MaskedEditType.Number;
mee.InputDirection = MaskedEditInputDirection.LeftToRight;
mee.TargetControlID = "txt_name";
Panel1.Controls.Add(mee);
.aspx code:
<asp:scriptmanager id="ScriptManager1" runat="server" xmlns:asp="#unknown">
</asp:scriptmanager>
<asp:panel id="UpdatePanel1" runat="server" xmlns:asp="#unknown">
</asp:panel>