That is not very high. The most common cause of a higher heartrate is dehydration.
If you are concerned get a checkup.
I meant to say 105 is not terribly high. Normal can go up to 100. 104 is only slight above that and could be normal for you.
104 is terribly high but you should get checked out by a doctor just to be sure. It is likely nothing to be concerned about but you should have a full blood panel to make sure all is in order. So just go and see the doctor for a check up.