What does it mean to say that the condition of chemical equilibrium is a dynamic situation?

Well when a see-saw is at equilibrium nothing moves. That is a static equilibrium - when the weights at either end balance and are unmoving. A is not the same - both the forward reaction and the backward reaction are constantly happening, they just balance each other out so it all looks static but isn't.

An easy way to see a is to run water from a tap strongly into a sink or bath with the plug hole open. Run it for a while and watch the water level stabilise until it no longer moves up or down.

Water is running in from the tap and water is running out down the plug-hole but the water level doesn't change - it is at a dynamic equilibrium.