Could I have a virus on my external hard drive?

Yes and yes (potentially, it depends on the type of virus you have). I have reinfected clean machines via exactly this method, although it was a thumb drive.

I ended up resolving my situation by downloading an anti-virus and running it a few times till the problem was gone… not sure how to resolve it without you infecting your machine, hope others can help :)

Well, a computer virus is typically some bit of code that embeds itself in a file or boot sector of a disk or some other area. When read, it can then spread itself to other places or deliver its payload.

The term virus is often misused in reference to trojans, worms, malware, adware, etc. even in the technical press.

Still, as you describe it – and in agreement with @dynamicduo – yes, since a virus can infect individual files or disks, you very well could have a copy on your external hd.

If you’re on a Windows-based PC, I’d be surprised that a regularly scheduled scan by your anti-virus software hasn’t turned the guy up yet. (But then, I’m assuming that if you’re on a Windows PC, you’d have anti-virus.)

Chances of finding a virus are high!
The solution get yourself a good antivirus, scan your whole computer and let it remove all viruses from your PC.
Done, plug in the external device, scan it for viruses using the antivirus program, and let it remove all viruses!

AVG 8 would be a great bet to try; and it’s free.

As everyone else has stated yes.
But in the case of the post above don’t use AVG 8 when AVG 8.5 is better and still free .

The Conficker worm is known to propagate through attached storage, notably thumb drives. If you have it on an external drive, there will be an extra, specious entry in the autoplay menu for that drive.

Autoplay should be disabled for all external drives precisely for this reason. If you have Windows XP, the TweakUI Powertoy gives you a convenient means of disabling autoplay on all your external drives at once.

And, as always – if Mac is the answer, you don’t know what the question was.

@IchtheosaurusRex I agree, disabling auto play is the first thing you want to do. The next step would be to scan the drive with every security program you have and can think of. Their are programs that specifically scan for conflicker among others. Good luck;)