Could be many things - but the most likely is that your chain tension is too slack.
It’s extremely dangerous to work with a badly loose chain. If the chain comes off but remains in the drive sprocket the end of the chain can whip around and damage your right hand.
Most saws have a chain tensioner that works with a screw moving the bar forward to tension the chain.
If I’m right however and you didn’t already know about chain tension, you need to put the chainsaw down and go and get some training before you injure yourself or someone else.