Can you install antivirus in a USB?

I mean to install it as if u have installed in your computer, but in the USB.

Big huge advice if there is a portable antivirus then its weak. don't install antiviruses except these becoase if you have weaker then no use viruses will strike. beleave me.
list of advised antiviruses:
* NOD32 "The best antivirus ever it gives you freedom & removes the most powerfull trojans" it automatically updates & does everything.
* Kaspersky "it is great but it doesn't let you access the internet freely"
* BitDeffender "stupid interface but strong"
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summery all strong so the best choice is NOD32 where all of the problems are fixed without annoying or notifying u.

no.. lol..

but you can use your anti virus on the computer, to scan the files on the USB

yes, go to www.portableapps.com, there is an antivirus you can use with the portable platform

Yes - they're called U3 security apps. There are many portable versions of antivirus, antispyware, and other programs that can be run right off the usb stick.

Yes there are some antivirus where you have to copy paste in your USB.. no need of installation and adding your entries to registry etc... take help of google to search antivirus

If you have an external USB hard-drive, you can install the files onto your USB drive in order to save up space on your hard drive. But whenever you unplug the USB drive, your anti virus won't work becase all the proper files are on the USB drive. So yes to your question!! Good Luck!!