Almost all standard bi-directional port pins on 8051's (excepting those that are truely open drain) will tend to turn on an N-Channel FET right at power-on. The weak pulup in these parts can easily bias the gate to turn on a part like you have been trying. Adding an external pullup will only make it easier to turn the parts on at initial power up.

If the intent is to avoid turming the N-FET's on at powerup time (until such time that the startup firmware is able to clear the corresponding port bits) then there are several choices:

1) Add an inverter (such as 74HC14) between the MCU pin and the N-FET gate.

2) Add a PNP transistor between the port pin and the N-FET gate to invert the drive signal to the gate.

Michael Karas