The electrical properties and electromagnetic shielding effectiveness of raw, dyed and softened, and treated with an antibacterial finish polygiene VO-600 cotton/antistatic polyester fabrics of two knit patterns, such as 1 × 1 rib and half-Milano rib, giving a very similar appearance for the fabric surface and having four polyester percentages (10%, 20%, 30%, and 35%) were investigated. Surface and the volume resistivity were measured according to EN 1149, and the effectiveness of electromagnetic shielding was determined according to ASTM D4935-18. The effect of individual factors (fiber composition, knit pattern, technical side, and treatment) and their complexity on the electrical properties of fabrics was evaluated by applying analysis of variance. The research revealed that the fiber composition of fabrics as an individual factor has the greatest influence on electrical properties. Electrical resistance decreased with the increasing percentage of polyester. Half-Milano rib fabrics were significantly more resistant than 1 × 1 rib fabrics. Raw fabrics were less electrically resistant than dyed and softened fabrics, and treated with antibacterial finish fabrics. Antibacterial finished fabrics were more electrically resistant than dyed and softened fabrics. The analysis of variance revealed that the complexity of investigated factors, such as fiber composition, knit pattern, and treatment, has a significant impact on fabric resistivity for both technical sides. Therefore, when selecting knitted fabrics with a very similar appearance for final applications in daily clothing, not only the impact of individual factors on their performance must be evaluated. The shielding effectiveness of the fabrics was too low to protect against electromagnetic waves.