Q: Can a falling body on earth exceed its terminal velocity in a huge vacuum container? Im not so sure about why a body has a terminal velocity. According to my knowledge it is due to the air drag. Force created by a falling body as it accelerates downwards due to gravity when equals the air drag then the body stops to accelerate and seems to continue at a constant terminal velocity. So if there is no air then due to no air drag this barrier can be broken right?  

A: 
if there is no air then due to no air drag this barrier can be broken right?

First, Terminal velocity is not a "barrier." It merely is an equilibrium state toward which the system tends. An object moving toward the ground at less than its terminal velocity will tend to speed up, and an object moving toward the ground at a greater speed (hardly ever happens, but the experiment could be performed) would tend to slow down.
So, let's re-word your question:

If there is no air then will a falling eventually exceed its terminal velocity?

No. Because of what "terminal velocity" means. It means, "the equillibrium speed toward which the object's motion will tend."  It's a function of the air density among other things.  The less dense the air, the higher that speed will be.  I don't know the formula, but intuitively, if there is no air (i.e., if the air density is zero), then the terminal velocity of the object will be infinite.
A falling object never will achieve infinite speed.

A: 
Force created by a falling body as it accelerates downwards

The drag force on a body is created by the fluid the body moves through and depends on, among other things, the velocity of the body but not the acceleration of the body.  The drag force is in the opposite direction of the velocity.
In the case of a body falling in a gravitational field through the air, the drag force is upward and increases as the downward velocity increases.  It follows that there must be particular downward velocity for which the upward drag force is equal in magnitude to the downward gravitational force.
When a body is falling through the air at this particular velocity, the net downward force is zero and so the body no longer accelerates (the velocity of the body does not change).  This particular velocity is called the terminal velocity and is not a characteristic of the body but rather, of the body and the fluid it moves through.
If there is no air there is zero drag force regardless of the velocity of the body and so there is no velocity for which the gravitational force is cancelled by a drag force.
