Red spotty rash in well 8 month-old

My 8 month old son having red spot rashes in face and arms and few
> in
> legs alone.
> No fever and the baby is active all the day.
> What could be this rashes as this is bothering m a lot?

As he is well, I would not be too concerned. There are a multitude of
possible causes but by far the most common are insect bites. As I don't know from where you are writing, it is hard to guess which is the most likely.
I would spray the mattress with a non-toxic (ie safe for humans) insect spray. If mosquitoes are likely then spraying the corners of the room where they meet the ceiling may help.
If the problem continues you should see your local doctor.
Please tell me what happens.