Add following css on page.

<style>
.ui-autocomplete-loading { background:url('http://www.ajaxload.info/cache/FF/FF/FF/00/00/00/38-0.gif&#039😉 no-repeat right center }
</style>

You can replace gif file with your desired image.

This image is more prominent,

<style>
.ui-autocomplete-loading { background:url('http://www.ajaxload.info/cache/FF/FF/FF/00/00/00/4-0.gif&#039😉 no-repeat right center }
</style>

Thanks Sir , This syntax only works on inline-insert so how applied in a pop-up insert …?

Try using !important at end.

<style>
.ui-autocomplete-loading { background:url('animation.gif') no-repeat right center !important }
</style>