Hi ShihabKhan,

Clear jQuery AutoComplete TextBox when no match found

Refer below example.

HTML

<script type="text/javascript" src="http://ajax.aspnetcdn.com/ajax/jQuery/jquery-1.10.0.min.js"></script>
<script type="text/javascript" src="http://ajax.aspnetcdn.com/ajax/jquery.ui/1.9.2/jquery-ui.min.js"></script>
<link rel="Stylesheet" type="text/css" href="http://ajax.aspnetcdn.com/ajax/jquery.ui/1.9.2/themes/blitzer/jquery-ui.css" />
<script type="text/javascript">
    $(function () {
        $("#txtSearch").autocomplete({
            source: function (request, response) {
                $.ajax({
                    url: 'Default.aspx/GetFruits',
                    data: "{ 'prefix': '" + request.term + "'}",
                    dataType: "json",
                    type: "POST",
                    contentType: "application/json; charset=utf-8",
                    success: function (data) {
                        if (data.d.length > 0) {
                            response($.map(data.d, function (item) {
                                return { label: item.Text, val: item.Value };
                            }))
                        } else {
                            response([{ label: 'No results found.', val: -1 }]);
                        }
                    }
                });
            },
            select: function (e, u) {
                if (u.item.val == -1) {
                    $(this).val("");
                    return false;
                }
            }
        });
    });
</script>
Enter search term:
<input type="text" id="txtSearch" />

C#

using System.Collections.Generic;
using System.Data.OleDb;
using System.Web.UI.WebControls;

public partial class _Default : System.Web.UI.Page
{
    [System.Web.Services.WebMethod]
    [System.Web.Script.Services.ScriptMethod()]
    public static List<ListItem> GetFruits(string prefix)
    {
        List<ListItem> fruits = new List<ListItem>();
        string str = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=D:\\Fruit.accdb;Persist Security Info = False; ";
        OleDbConnection con = new OleDbConnection(str);
        OleDbCommand cmd = new OleDbCommand("SELECT FruitId,FruitName FROM Fruits WHERE FruitName LIKE '%' + @Fruit + '%'", con);
        cmd.Parameters.AddWithValue("@Fruit", prefix);
        con.Open();
        OleDbDataReader odr = cmd.ExecuteReader();
        while (odr.Read())
        {
            fruits.Add(new ListItem { Text = odr["FruitName"].ToString().Trim(), Value = odr["FruitId"].ToString().Trim() });
        }
        con.Close();

        return fruits;
    }
}

VB.Net

Imports System.Collections.Generic
Imports System.Data.OleDb

Partial Class Default
    Inherits System.Web.UI.Page

    <System.Web.Services.WebMethod()> _
    <System.Web.Script.Services.ScriptMethod()> _
    Public Shared Function GetFruits(ByVal prefix As String) As List(Of ListItem)
        Dim fruits As List(Of ListItem) = New List(Of ListItem)()
        Dim str As String = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=D:\Fruit.accdb;Persist Security Info = False; "
        Dim con As OleDbConnection = New OleDbConnection(str)
        Dim cmd As OleDbCommand = New OleDbCommand("SELECT FruitId,FruitName FROM Fruits WHERE FruitName LIKE '%' + @Fruit + '%'", con)
        cmd.Parameters.AddWithValue("@Fruit", prefix)
        con.Open()
        Dim odr As OleDbDataReader = cmd.ExecuteReader()
        While odr.Read()
            fruits.Add(New ListItem With {.Text = odr("FruitName").ToString().Trim(), .Value = odr("FruitId").ToString().Trim()})
        End While
        con.Close()

        Return fruits
    End Function
End Class

Screenshot