Can you install the Frame directly to the block (Concrete) Wall?

It is possible to install a prehung entry in the block wall But be concerned with moisture from the block or the concrete walls. The first step is to see what is the code requirement from the Building department.  

You have two options:

1. You need to Control the Moisture when installing directly to the block walls. You can use available Moisture barriers. They are available in rolls. Your rough opening might be the same if you are using this method. 
2. You can install the Treated Wood to the concrete/Block Walls prior to the frame installation. Please note the rough opening changes if you use this method.