No, you can't log in two from the same account.
But that did give me an idea, it would be nice to be able to force a toon off so you could log another one on from a different location. Since I travel alot I leave some toons boxed at my home and I control them from the road. Occasionallly a toon will get kicked to char. select screen but stay logged in. Now that account is dead until I can get someone to deal with it at my house...