N-methyladenine (mA) is the most abundant RNA modification in mammalian messenger RNAs (mRNAs), which participates in and regulates many important biological activities, such as tissue development and stem cell differentiation. Due to an improved understanding of mA, researchers have discovered that the biological function of mA can be linked to many stages of mRNA metabolism and that mA can regulate a variety of complex biological processes. In addition to its location on mammalian mRNAs, mA has been identified on viral transcripts. mA also plays important roles in the life cycle of many viruses and in viral replication in host cells. In this review, we briefly introduce the detection methods of mA, the mA-related proteins, and the functions of mA. We also summarize the effects of mA-related proteins on viral replication and infection. We hope that this review provides researchers with some insights for elucidating the complex mechanisms of the epitranscriptome related to viruses, and provides information for further study of the mechanisms of other modified nucleobases acting on processes such as viral replication. We also anticipate that this review can stimulate collaborative research from different fields, such as chemistry, biology, and medicine, and promote the development of antiviral drugs and vaccines.