Reactivity and aromaticity of DNA and RNA bases toward an external electric field are analyzed using density functional theory (DFT) and density functional reactivity theory (DFRT). Reactivity of the nucleobases is measured in terms of the DFT-based reactivity descriptor, such as energy of the HOMO, global hardness, electrophilicity, etc. and is observed to be sensitive toward the strength as well as direction of the applied external electric field. In addition, the reactivity pattern follows the maximum hardness and minimum electrophilicity principles. Further, aromaticity of the species is observed to be effected by the presence of an external electric field.