I am H1B employee of company A.
I am doing full-time job in company B now after doing H1B transfer.
I was wondering if I can do another full-time job with company C again doing H1B transfer(I am being accepted with company C as well).

Gohtalo,

Under H1-B rule, you can have H1-B approval from multiple companies. However, you can not have multiple payroll at a time. What this means is one employment at a time. You can have active H1 from company A to Z at a time but can only work for one company.

From what I understand of ur case; yes is the answer to your question.

GoodLuck.

the_dude,
I mean doing two jobs simultaneously.
One remotely and one on-site at same time,may be one after work hours.

Nop.

H1-B rule says: Strictly one company [payroll] at a time. Yup it sucks that you don't have this freedom until u get your EAD or Green Card rather to be more specific. I know this is not the favorable answer but this is the reality. There has not been any reform talks yet and I don't see this rule changing anytime soon. I don't know ur situation but if u have good connection with both companies you can make them work out C2C and have only one company run your salary. There are lots of ways to get around but depends on your relationship with these companies.

GoodLuck.