Generally it is allowed. Your outstanding will show in negative OR your credit limit will increase.what if I pay more than my credit card bill?
Eg, if your credit limit is 50,000 and you have paid excess 2,000, then your credit limit will be 52,000 for the next cycle (its your own money)
However banks might have restrictions on how much excess payment can be done as one may pay excess cash (obtained by illegal means) to credit card account bill. Or maybe cash payment in excess may not be allowed at all.