Antivirus for mac OS X v10.9.5?

None needed.

But if you want to stay secure on OS X 10.9.5 Mavericks, you need to STOP using that 3-4 year old version of the Safari Web browser and switch to a Web browser that is up to date, like Mozilla Firefox OR Waterfox.

Good Luck to You!

No Anti-Virus software or so-called “cleaning” apps are needed or recommended for Mac OS. They can conflict with Mac's own built-in security. At best they will slow your Mac by using unnecessary resources and at worst will bork your entire system.

There had been no issues with adware, malware, or viral attack in 10.9(.5)

although I did install a new 10.11.6 on second partition last September, of

system I had held off on for a year. Seems enough dust had settled for me.

While my Mac (mini i7 server) has second unused internal HDD, I'm pausing

to consider later macOS versions it may support before allowing them to take

up residence inside there; no telling how my Late 2012 model may like them.

..And at least one security update for El Capitan + Safari happened this year..

Be sure to backup at least two or three ways'/means before upgrading further.