Server has antivirus. Do I need to enable external locking on MySQL? From MySQL docs: 


  If you only read tables with other programs, external locking is not required 


Assuming the bytes of MySQL files does not match viruses, the antivirus will not change the contents of the file.

However, the antivirus may change file attributes and "do some other things".

Do I need to enable external locking on MySQL to prevent (possible) data corruption?

(I'm using both InnoDB and MyISAM.)
No, external locking is (was) only needed for MyISAM when you tried to execute several processes on the same data directory, such as two server instances, or an instance and a file repair.

Sincerely, I would be surprised if that page manual was accurate and was still fully supported. In any case, it is mostly impossible to do that now, as InnoDB (default engine) disallows 2 instances on the same server at the same time.

In summary, an antivirus scan is not a problem for MySQL, unless it changes the files or moves them away; and if the resources it uses do not interfere with the database execution. I wouldn't run, however, an antivirus software on a production server, unless it was for scanning the network (emails or desktop clients).