You don't mention whether the ant is jsut starting out from rest or moving steadily across the floor. I will assume the latter case.
The definition of acceleration is the time rate of change of motion, that is, change of speed, v, with time t, or mathematically dv/dt.
If the ant is moving across the floor at a constant speed - as ants typically do - then, there is no change of speed and so dv = 0.
Therefore, the ant's acceleration is zero.