Ajax - Jquery Event Fires Twice

I've got the an bit of ajax and the succeed runs twice. I've got a global var that I used to keep track.

Code:
var counter = 0
$('#txtLookupText').keyup(function(event) {
$(document).ready(function() {
});
$.ajax({
type: "POST",
url: 'ContactLookup.aspx/LookupContacts',
data: "{'inputStr': '" + $('#txtLookupText').val() + "'}",
contentType: "application/json; charset=utf-8",
dataType: "json",
success: function(msg) {
AjaxSucceeded(msg);
},
error: AjaxFailed
});
});
function AjaxSucceeded(result) {
if (result.hasOwnProperty("d")) { result = result.d; }
var li = ''
for (i = 0; i < result.length; i++) {
li += result[i].FirstName + ' ' + result[i].LastName + '
}
counter += 1
alert(counter)
}
function AjaxFailed(result) {
alert(result.status + ' ' + result.statusText);
}

I moved the counter to the POST and only got one alert box. In the succeed, I get 2 alert boxes in succession.