jQuery Validate Form

$("#FORM_NAME").validate({
    errorClass: 'error_text',
    errorElement: 'span',
    highlight: function(element, errorClass, validClass) {
        $(element).parents("span").addClass(errorClass);
    },
    errorPlacement: function(error, element) {
        error.insertAfter(element);
        element.focus(); // <- this line is causing your whole problem
    },
    rules: {
        "mobile": {
            required: true,
            digits: true,
            minlength: 10,
            maxlength: 10
        },
    },
    messages: {
        "mobile": {
            required: "Mobile No is Required.",
            digits: "Please Enter Digits, Not Characters."
        },
    }
});
var validate = $("#FORM_NAME").valid();
if (validate == true) {
    var formData = new FormData($('#FORM_NAME')[0]);
    formData.append('lang', lang);
    ajaxCall = $.ajax({
        url: 'SITE_URL',
        type: 'POST',
        data: formData,
        cache: false,
        contentType: false,
        processData: false,
        success: function(data) {
            var res = JSON.parse(data);
            if(result.type == 'success'){
                //Message
                alert(result.message);
                // $('#FORM_NAME').trigger("reset");
            }else{
                //Message
                alert(result.message);
            }
        },
        statusCode: {
            404: function() {
                alert("page not found");
            },
            403: function() {
                alert("Forbidden");
            },
            500: function() {
                alert("Internal Server Error");
            }
        }
    });
}