How should the accelerator/throttle be like on a dirt bike?

My cousin has a dirt bike and when you turn it on, if its in neutral or the clutch is in, you have to keep accelerating for the bike to stay on, should dirt bikes be like that, do they run better like that, i would say maybe that it's meant for racing bikes because if it was for FMX (freestyle motocross) bikes then when in the air, their bike would turn off.

There is nothing wrong with the bike, its not dirty or anything like that, it has been added on the bike to be like that, just letting you know.

Is it a 2 stroke or 4 stroke.
generally 2 strokes aren't supposed to idle so they won't foul sparkplugs.

No it deffinetly should be like that, unless it has the choke on. When you stop throttling it in Neutral, it should idle for about 10 seconds and then shut off. When the FMXers are in the air, they're giving the bike gas, too.

but then again I own a 2-stroke

I would agree with Bikerwoody. the carb wants set up. could simply need the idle turned up or may need new jets. take it to a mechanic and get it set up.
it could be a stretched throttle cable, may just need adjusted.

No, the bike should idle when the throttle is released, not stall. The carburettor is probably dirty or not adjusted right.