do i need antivirus using ubuntu

If you are sharing your files with windows machines, it doesn't hurt to have some antivirus.

Welcome aboard.

No, you don't need antivirus software on Linux or BSD.

no BUT !!! maybe yes

if say you are running Fedora or RHEL and did NOT disable SELinux

there is really NO virus that is able to " Also run on linux" that can install
-- or if in your home folder then a reboot uninstalls it

BUT
if you share things with OTHER people on Windows machines and they share with YOU
you can be a carrier -- just like " typhoid Mary "

for those
Scan using the FREE and ALREADY in your distros repos
"ClamAV "

so for ubuntu
then read the instructions on the clam web site

As you can tell from the replies, only you can really decide.
Linux is more resistant to viruses then Windows (last time I read, something like three viruses, rarely seen), but that isn't the only issue that Windows users face.
Both can get rootkits, etc. A lot of that deals with your security practices.

As stated, if you setup your Linux box, as a network share for a bunch of Windows users, antivirus could help catch things your Windows users choose to share over the network.

note:
should read:
"viruses" do exist for linux and attacks can be targeted to include multiple o/s's but most target Msoft PC's because this is the easiest method.
Clamav will clear out stuff that will affect your windows using friends that you share files with, however, it is not like a constantly running anti-virus on windoze, you have to run it as a scan. That said you can run it as an active email scanner, not much use if you don't use an email client.
Best way to keep a linux system clean is to keep it updated. You don't have to go outside of protected areas to get software and that is a great bonus.

Fred.

I have run Linux as my primary operating system for about 15 years (Meaning... no dual booting with Windows,... Only 1 Windows system around for "just in case purposes" [flashing roms, setup for devices with no Linux support, etc.]). I played with it for several years before that. In all that time I have neither run an anti-virus program on my Linux systems, nor have had myself attacked remotely. I will say that I keep my systems updated.

Your biggest threats when running Linux are social engineering attacks (weak passwords). Secondary to that is enabling SSH and not modifying the port... Telnet should never be used (by default, it is disabled on just about all major distros). Third, running apps that you get from 3rd party repositories, that cannot be trusted (you wouldn't need run many 3rd party repositories, and really never would need to run one that isn't from a trusted source).

My take on this:

It never hurts to have protection, even if the system is, by nature, moderately immune.

ClamAV is currently the best recommended, and can protect you fairly well. Even though Viruses and such malware target Windows, there are some that now target Darwin, BSD, and Linux based systems, and the damage these can do can be catastrophic, at times. Most of the ones targeting Darwin based systems, like Apple/Mac OS-X, target firmware and other embedded systems in computers. Linux and BSD normally get rootkits. Remember, even with AppArmor, SELinux, and other built-in stuff, nothing is 100 percent.

My recommendation, if you think you need it, get it.

ClamAV + rkhunter + iptables can protect you very well. I run ClamAV daemonized along with iptables, and have rkhunter ran via a cronjob at regular intervals. I haven't had any issues, yet, but I'd rather drop a few CPU cycles and a small chuck of RAM and be safe than sorry.