Do you need an antivirus on Linux?
Linux's permission system prevents users from performing operations on system files or files owned by other users without permission. Even users with sudo access will need to enter their password before elevating their privileges.
This enforces a stricter security boundary than on Windows between system and userspace files, making it more difficult for a malicious file downloaded and opened through an email client or web browser to infect an entire system. This permissions' boundary is also why it's generally a bad idea to run any services or processes as root on Linux, and those that do might voluntarily de-escalate their permissions (i.e. startup as root to configure themselves, then step down their permissions to another user) in order to protect the system if they're compromised.