In the present work, we report on the effect of carbon atoms on the core structure and mobility of screw dislocations in body-centered cubic iron (Fe) using classical interatomic potentials available in the open literature. The interatomic potentials employed are selected based on their ability to reproduce the correct dislocation characteristics in iron. Carbon atoms are introduced at two sites in the dislocation core for understanding the effect of solute position. Reconstruction of dislocation core from easy to the hard core configuration is observed irrespective of the initial position of the carbon atom, which eventually settles in the prismatic sites formed by the rows of Fe atoms in the hard core. Loading is carried out parallel and perpendicular to the Burgers vector to understand the effect of carbon on the non-Schmid characteristics of the slip. Twinning-antitwinning (T/AT) asymmetry of CRSS is observed when the dislocation core symmetry of the easy core configuration is retained after the core reconstruction occurs. The CRSS of dislocation in both easy and hard core configuration is sensitive to the loading conditions. Asymmetry in CRSS and choice of glide planes are correlated with the dislocation core spreading onto the {1 1 0} planes in the zone under the influence of the applied loads.