© 2021, The Author(s). Objective: This study describes the occurrence of a silent mutation in the RNA binding domain of nucleocapsid phosphoprotein (N protein) coding gene from SARS-CoV-2 that may consequence to a missense mutation by onset of another single nucleotide mutation. Results: In the DNA sequence isolated from severe acute respiratory syndrome (SARS-CoV-2) in Iran, a coding sequence for the RNA binding domain of N protein was detected. The comparison of Chinese and Iranian DNA sequences displayed that a thymine (T) was mutated to cytosine (C), so “TTG” from China was changed to “CTG” in Iran. Both DNA sequences from Iran and China have been encoded for leucine. In addition, the second T in “CTG” in the DNA or uracil (U) in “CUG” in the RNA sequences from Iran can be mutated to another C by a missense mutation resulting from thymine DNA glycosylase (TDG) of human and base excision repair mechanism to produce “CCG” encoding for proline, which consequently may increase the affinity of the RNA binding domain of N protein to viral RNA and improve the transcription rate, pathogenicity, evasion from human immunity system, spreading in the human body, and risk of human-to-human transmission rate of SARS-CoV-2.