As of now, no we don't, as the "virus community", if you will, hasn't yet released viruses on a large scale for Android. But it is a given that in the future, viruses attacking the Android system will definitely be made - its status as the most used mobile OS ensures that. Just remember that the sole reason that viruses are abundant for Windows only, and not for Mac and Linux, is the fact that Windows is still the overwhelming choice of OS around the world, hence making the time invested by the virus-maker worthwhile.
Most viruses rely first and foremost on the user's complicity. Most of them can't just function on there own. For example, you have to download an infected email, or install an infected software to really allow the virus to function - you get the gist. To be fair, Android is a much more tightly-knit OS than Windows, as performing even very small tasks requires the user's permissions. Also, the apps run in a sandbox, separated from the system, so there is a very low chance of infected apps ruining the system. But there are a hell lot of ingenious coders out there, who would certainly find ways to infect your phone.