"I'm on the way" also means "I'll be there shortly" in chinese: 我在路上 (I'm on the road/street) - implying that you're now walking your way towards a particular place or to someone. :)

我已經在路上啦﹗

just on the way to find a happy garden

If you are asking about the meaning of "I am on the way", it means, "I am coming immediately" or "I am already traveling to you."

Where are you going? Now,come to my hometown,hehe