If you are using a windows-based device, yes, you need an annual based licensed antivirus.
If you are using an Apple device, you do not need any antivirus software. But you do need an adware or spyware blocker.
An Antivirus solution is best installed right after your computer has been formatted. It acts as a security guard. It takes a snapshot the files that are already inside your system and then it keeps a lookout for strange behavior caused during installations and captures the process and infecting file source and quarantines it, where it can do no more harm. So ideally when your computer gets infected, if you install an antivirus solution after that, it will not make much difference. It needs to be formatted first. As soon as a computer is formatted, Antivirus needs to be installed right away, failure to do so will leave the device open to threats and viral infection. If you have decided to backup content before formatting, all backups and USB drives need to be scanned for viruses and threats so as not to re-infect the system by copying the data content once more.Antivirus software should not consume excessive memory. Antivirus should not be intrusive, and it must not disturb the user.