Codon usage bias (CUB) could reflect co-evolutionary changes between viruses and hosts in contrast to plant and animal viruses, and the systematic analysis of codon usage among the mycoviruses that infect plant pathogenic fungi is limited. We performed an extensive analysis of codon usage patterns among 98 characterized RNA mycoviruses from eight phytopathogenic fungi. The GC and GC3s contents of mycoviruses have a wide variation from 29.35% to 64.62% and 24.32% to 97.13%, respectively. Mycoviral CUB is weak, and natural selection plays a major role in the formation of mycoviral codon usage pattern. In this study, we demonstrated that the codon usage of mycoviruses is similar to that of some host genes, especially those involved in RNA biosynthetic process and transcription, suggesting that CUB is a potential evolutionary mechanism that mycoviruses adapt to in their hosts.