Although virus's havent been the mainstream headline grabber for Android yet, rogue apps are, specifically those containing malware.
Call it "peace of mind" when you install an anti-v on your device. You must remember, The Android Market, unlike apple's market, does not certify apps before developers submit them for distribution. The Android Market will wait until people complain before they remove an app.Usually it is Malware.
In theory, ant-v apps are supposed to scan an app after installation. Also, they have device tracking features and some other useful items.
There are several on the market, some free along with their paid versions.
I use AVG as they've been around for awhile.