Reinforcing strategy by adding nano- and/or micro-scale fillers leads to enhanced not only mechanical properties of 3D-printed parts but also viscoelastic properties such as creep behavior. To characterize this complex creep behavior of composite materials, viscoelastic mathematical models are used combined with experimental data. As a preliminary study, neat polyetherimide (PEI) and 5, 10, 20 wt.% CB reinforced PEI composite filaments were fabricated in the co-rotating twin-screw extruder. After rheological examinations, dynamic mechanical analysis (DMA) samples were printed by a custom-made 3D printer to realize creep analysis. In this study, the Burgers model and the empirical Findley power-law model were employed to simulate the experimental creep data. Both of the models were able to simulate the experimental data in good agreement. However, the Burgers model could not capture the elastic instantaneous strain but the Findley power-law model gave more agreed curve fits.