There are two ways for it::
1st one is:
<asp:label id="Label6" runat="server" forecolor="White" width="200px" xmlns:asp="#unknown"></asp:label>
<script>
function settext()
{
var name = document.getElementById('<%= txtbox1.ClientID %>').value;
document.getElementById('<%=Label6.ClientID%>').innerHTML = name;
}
</script>
2nd one is
<asp:label id="Label6" runat="server" forecolor="White" width="200px" ClientIdMode="Static" xmlns:asp="#unknown"></asp:label>
<script>
function settext()
{
var name = document.getElementById('<%= txtbox1.ClientID %>').value;
document.getElementById('Label6').innerHTML = name;
}
</script>