Getting a label value using jquery.

I have a label inside an Ajax Modal Popup Extender.

Here is my code:

<asp:GridView ID="gvEvaluation" runat="server" DataSourceID="SqlDataSource3"
                            CellPadding="0" BorderStyle="None" BorderWidth="0px" AutoGenerateColumns="False"
                            EnableViewState="true" DataKeyNames="Task_No, Activity_ID" GridLines="None"><Columns><asp:TemplateField HeaderText=""><ItemTemplate><div class="col-md-12"><table class="table table-bordered  table-condensed" width="800" style="table-layout: fixed;"><tbody><tr class="kpitblrow2"><td width="110"  ><asp:UpdatePanel ID="UpdatePanel1" runat="server"><ContentTemplate><asp:LinkButton ID="lkActivityFiles" runat="server" class="btn btn-success btn-xs "
                                                                        CommandArgument="<%# CType(Container, GridViewRow).RowIndex %>" CommandName="ViewEditActivityFiles">  View / Edit </asp:LinkButton><asp:ModalPopupExtender ID="lkActivityFiles_ModalPopupExtender" runat="server" PopupControlID="pnlActivityFiles"
                                                                        BackgroundCssClass="modalBackground" CancelControlID="btnHide"
                                                                        Enabled="True" TargetControlID="lkActivityFiles"></asp:ModalPopupExtender><asp:Panel ID="pnlActivityFiles" runat="server" CssClass="modalPopup"><h5 ><asp:Label ID="lblActivityIDHeader" runat="server" Text='<%# Eval("Activity_ID") %>'></asp:Label><asp:Button ID="btnHide" runat="server" Text="x" Font-Bold="true" OnClientClick="return HideModalPopup()"
                                                                                        CssClass="btnclose" OnClick="btnHide_Click" /></h5>

How can I get the value of  the label, lblActivityHeader using jquery?