If you mean the screw has a 6-point star for it's head, that's a Torx screw, and you'll need a torx bit to put it in.
Airsoft typically don't use those...so either it was a screw that was added to replace one that was lost, or was dropped in by accident. Most airsofts use Philips and Allen (hexagon head) screws.
Look around in your gun and see if you can find out where it went, if not, then game on.
As a reference, here's a description of some screw types....it may help you later in life:
security screws will have a post in the middle of the head, so that you need special bits to get them out.
slotted .. it's just a slot
tamper-proof slotted .. slotted but it has ramped cuts in one direction so that you cannot unscrew it without great difficulty, usually public restroom stalls use these.
philips .. looks like a plus sign
allen .. hexagon
Torx .. 6-point star
Nintendo .. 3-point version of philps, think a mercedes-benz emblem I don't know the right name, but Nintendo was the first company to use these widely.
robertson .. square hole