If you are ordered to pay a set amount of money each month on the arrearage, the fact that you get a bonus should not change the amount you are paying monthly. However, if you are being taken back to court to modify support or to modify the arrearage payment, a judge can certainly order that it be taken to pay the arrearage.
Unfortunately, if you have an arrears balance, a bonus check (and any other lump payment like a settlement or a tax refund) can be garnished. If the case is enforced by child support enforcement this is more likely to happen. If it is simply a case where you pay the other party directly, the other party or their counsel will have to file something with the court before they can garnish the check.