When painting your brick fireplace be sure to use a latex based heat resistant interior paint that is either flat or semi gloss paint for the brick fireplace.
The paint for your brick fireplace should be a paint that is rated to withstand a minimum of 200 F degrees which is around what a fireplace generates in heat.
You should also paint the brick fireplace using a roller that is designed to paint textured surfaces so it will give it a lovely paint job.
If you use non heat resistant paint on your brick fireplace it's likely to peel off from the heat that is generated from the fireplace overtime.