3D printing technology could be extremely beneficial for increasing the flexibly and reducing the cost of carbon fiber reinforced polymer composite (CFRP) production. However, this technology suffers from poor surface quality and uncertain engineering quality. Mechanical finishing processes could concurrently solve these surface issues with the 3D printed composites components. Herein, a mechanical finishing process for 3D printed CFRP composites via CNC milling is proposed to improve the surface quality of two 3D printing methods, namely fused deposition modeling (FDM) and laser assisted-laminated object manufacturing (LA-LOM). The 3D printed CFRP structures fabricated via both methods comprise of continuous carbon fiber reinforcement. The surface roughness and surface morphology of the original unfinished and finished surfaces with various cutting depths are extensively studied to investigate the feasibility of the proposed finishing technique. The surface morphology of the surfaces parallel and perpendicular to the 3D printed layers is the main focus of this work. After the CNC finishing process, the surface roughness of the 3D printed CFRP composites is improved by 70% and 60% for FDM and LA-LOM components, respectively. A smooth, consistent, and predictable surface morphology is achieved for various cutting depths demonstrating a substantial improvement over the original 3D printed surfaces.