Diagnosis of bovine viral diarrhea (BVD) relies on the detection of antibodies against its viral causing agent, bovine viral diarrhea virus (BVDV). Here, we designed a novel competitive ELISA (cELISA) using the most immunogenic part of BVDV nonstructural protein 3 (NS3), as a single ELISA recombinant antigen, along with a monoclonal antibody to detect antibodies against BVDV in sera of infected animals. Hence, 197 serum samples were tested by this cELISA and the results were compared to the results obtained from virus neutralization test (VNT) as the gold standard method for diagnosis of BVD. McNemar’s test indicated that there was no significant difference between the results of this newly designed cELISA and VNT. Meanwhile, kappa coefficients showed that there was a high correlation between these two assays. The relative sensitivity and specificity of cELISA with respect to VNT were 93.90% and 100%, respectively, suggesting that this newly designed cELISA could be a useful diagnostic tool for detection of BVDV infection. Moreover, as NS3 is highly conserved among Pestiviruses and the developed ELISA is a competitive one, it could potentially be applied to detect BVDV infection in other domestic and wildlife species.