I took oil filler cap off today while engine was running and air was blowing out of oil filler is this normal ?

 

it happens under the following conditions

an oil change was done without pre-filling the filter and the crank wasn't turned over by hand before firing it up....

i'm joking btw

 

All a question of degree. A tiny bit of detectable "breeze" is normal. A significant amount of air outrush, especially if accompanied by smoke or oil vapour, is probably something you need to investigate further.

If you're not sure how much is too much, have it looked at.