The asteroid posses effectively no threat to the planet itself or its earthlings as it's estimated to only be between 9-45m wide. It will be passing by incredibly closely at ~12000kms away, which is about 23 times closer to the Earth than the Moon is situated. However, it's reportedly traveling incredibly slow relative to Earth, approaching us at only about 1m/s. So even if it were on a direct impact with Earth it would more than likely break apart in the the atmosphere in a brilliantly massive fire ball with only a few small meteorites hitting the planet's surface.
|Trajectory of 2011MD|
For further information about the asteroid and its path hit up JPL's Solar System Dynamics website.