Hi,
I am working with London based company and receiving commission every month One Thousand(1,000.00) USD. Is I am liable to pay any tax? If yes, Please let me know how much?

WHERE do you live and work?

If you are U.S. citizen or resident, you must report this income on your tax return. This is self employement income and it is subject to SE tax. You will do schedules C or C-EZ (Form 1040) and SE (Form 1040).