In ASP.NET on client side? I hope you never achieve this.
But you can do inside your browser window:
<script type="text/javascript" src="http://code.jquery.com/jquery-1.9.1.js"></script>
<input type="text" name="name-field" id="name-field">
<script type="text/javascript">
$(function () {
$(document).keydown(function(e) {
e.preventDefault();
});
});
</script>