Arduino digital output

I have Pro Mini board (same 328 processor as Uno & Nano).
Using 2N7000 FETs as switches I was getting odd responses.
When other pins were outputting, Pin 9 would also give an output, sufficient to switch its FET even though Pin 9 is not written into the sketch.

Pin 9 was connected as I thought I might use it as the code developed.
I had used 1Meg gate pulldown resistors.
Another identical board did not exhibit this behavior.

I guess setting Pin 9 as output & writing low ought to fix it but for now I have disconnected the pin.

Show your circuit. Don’t just talk about it.

Grease from your hand left on the board may give enough conductivity to activate the MOSFET but it seems unlikely.

Is this a breadboard? Measure the resistance between the pins with your multimeter. You may have a poor connection on the ground pin of the Mini.