I'm checking valve clearances today and pulled the air filter for cleaning.

There is oil on the air filter and inside the air box.

I changed the oil last week and haven't had the chance to ride it but once. So I'm assuming the oil has been in there a while since it is dark brown oil.

I just wanted to know if this is normal or if I should check to see if there is something else going wrong.

Thanks for the help.

Comes from the valve cover breather tube. It's normal, unless it's excessive.