A brain infection or a brain abscess is possible from a root canal procedure if some part of the infection from your tooth leads and spreads to your brain.
But mos root canals are done very safely and most people come out of the root canal procedure with no harm done to them.
If you think you have a brain infection after the root canal you need to go to urgent care or the emergency room for treatment just in case.
It's very rare though that people get brain infections from root canals and your chance of getting a brain infection after a root canal is around 1 in 15,000 or more.