I smell something burning
Is that means something is burning now ?
Why I can't say that I smell something burnt.
thanks for your help

Question

I smell something burning 
Is that means something is burning now ?
Why I can't say that I smell something burnt. 
thanks for your help

Answer

Yes, it means that something is burning now and is continuing to burn.

Burnt is the past participle of burn - it's the past tense so it is no longer burning.