HIGH in input pin without connect
Put a pull-down resistor on it.

Floating (unconnected) inputs can move any way they want. The steady state (if it ever gets to a steady state) depends on the chip architecture, the PCB layout or other signals around it. 

However it is more worrying that you care about the state of something you have not connected. 



I just saw your comment about connecting it to another output source.

This means you have a non-problem: a problem that not really exists.
Connect it and it should all work.