Hi irshad1231,

Check this example. Now please take its reference and correct your code.

HTML

<table border="0" cellpadding="0" cellspacing="0" style="border-collapse: collapse">
        <tr>
            <td>First Name:</td>
            <td><asp:TextBox ID="txtFirstName" runat="server" /></td>
            <td><asp:RequiredFieldValidator ErrorMessage="*" ForeColor="Red" ControlToValidate="txtFirstName"runat="server" /></td>
        </tr>
        <tr>
            <td>Last Name:</td>
            <td>
                <asp:TextBox ID="txtLastName" runat="server" />
            </td>
            <td><asp:RequiredFieldValidator ErrorMessage="*" ForeColor="Red" ControlToValidate="txtLastName" runat="server" /></td>
        </tr>
        <tr>
            <td>Designation:</td>
            <td><asp:TextBox ID="txtDesignation" runat="server" /></td>
            <td><asp:RequiredFieldValidator ErrorMessage="*" ForeColor="Red" ControlToValidate="txtDesignation" runat="server" /></td>
        </tr>
        <tr>
            <td>Fruit:</td>
            <td>
                <asp:CheckBoxList ID="chkFruits" runat="server">
                    <asp:ListItem Text="Mango" />
                    <asp:ListItem Text="Apple" />
                    <asp:ListItem Text="Banana" />
                    <asp:ListItem Text="Pineapple" />
                    <asp:ListItem Text="Guava" />
                    <asp:ListItem Text="Grapes" />
                    <asp:ListItem Text="Papaya" />
                </asp:CheckBoxList>
            </td>
            <td><asp:CustomValidator ID="CustomValidator1" ErrorMessage="Please select at least one item."
                    ForeColor="Red" ClientValidationFunction="ValidateCheckBoxList" runat="server" />
            </td>
        </tr>
        <tr>
            <td>Address:</td>
            <td><asp:TextBox ID="txtAddress" runat="server" /></td>
            <td><asp:RequiredFieldValidator ErrorMessage="*" ForeColor="Red" ControlToValidate="txtAddress" runat="server" /></td>
        </tr>
        <tr>
            <td>Telephone:</td>
            <td><asp:TextBox ID="txtTelephone" runat="server" /></td>
            <td><asp:RequiredFieldValidator ErrorMessage="*" ForeColor="Red" ControlToValidate="txtTelephone" runat="server" /></td>
        </tr>
        <tr>
            <td>Email:</td>
            <td><asp:TextBox ID="txtEmail" runat="server" /></td>
            <td><asp:RequiredFieldValidator ErrorMessage="*" ForeColor="Red" ControlToValidate="txtEmail" runat="server" /></td>
        </tr>
        <tr>
            <td>&nbsp;</td>
            <td colspan="2">
                <asp:Button ID="btnSubmit" Text="Submit" runat="server" />
            </td>
        </tr>
    </table>

JavaScript

<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
<script type="text/javascript">
    function ValidateCheckBoxList(sender, args) {
        var checkBoxList = document.getElementById("<%=chkFruits.ClientID %>");
        var checkboxes = checkBoxList.getElementsByTagName("input");
        var isValid = false;
        for (var i = 0; i < checkboxes.length; i++) {
            if (checkboxes[i].checked) {
                isValid = true;
                break;
            }
        }
        args.IsValid = isValid;
    }
    function WebForm_OnSubmit() {
        if (typeof (ValidatorOnSubmit) == "function" && ValidatorOnSubmit() == false) {
            for (var i in Page_Validators) {
                try {
                    if (!Page_Validators[i].isvalid) {
                        var control;
                        if (Page_Validators[i].controltovalidate != undefined) {
                            control = $("#" + Page_Validators[i].controltovalidate);
                        } else {
                            control = $("#" + Page_Validators[i].id);
                        }

                        var top = control.offset().top;
                        $('html, body').animate({ scrollTop: top - 50 }, 800);
                        control.focus();
                        return;
                    }
                } catch (e) { }
            }
            return false;
        }
        return true;
    }
</script>

Screenshot