Can I transfer more balance to a cc with a balance transfer already on it?

Hello everyone just looking to get some info on this matter. I have an MBNA card that I’ve had a balance transfer on and am still paying it off. I’ve locked the card and solely use it to pay off the balance. My term ends in December but I received another balance transfer offer from them, so I’m wondering if I can transfer more balance even thought I have previous balance left. Thanks!