Yes, this is possible. It could be that you are entitled to the working income tax benefit (WITB). This is a refundable credit intended to provide tax relief for low-income working individuals and families. If you are eligible for this benefit, TurboTax will automatically calculate this credit based on the info provided on your return. For more info, please see http://www.cra-arc.gc.ca/bnfts/wtb/menu-eng.html
If you are just looking at the negative figure in the top bar, that amount is what is owing by the time you get to review.
There are a few other credits that are refundable. The children's activity credit and the refundable medical supplement come to mind too.