Sayang, at that age some babies do stare at their fingers as they're learning how things move and what their hands can do, it's actually quite normal development, especially if he's doing other things like responding to you, playing, and reaching for toys. That said, since you're noticing it enough to wonder, it might be good to mention it to your pediatrician during the next check-up, just so they can see how he's developing overall and put your mind at ease. Every child develops at their own pace, and a doctor can give you proper guidance better than anyone online.