Asynchronous continuation problem facing in callback

I am new to this camunda. I want to implement an asynchronous service task. where from ActivityBehavior execute method I am sending one message to activeMq. There is another MessageListener where consume the corresponding message from MQ and process it. After processing the message I want to send the signal to my activity. I am using the following code to send signal to my activity behavior.
runtimeService.signal(msg, callbackPayload);

But after calling this method what I observed is that it is calling my ActivityBehavior execute method again. As my Listener is running on a separate thread.
I want to know what is the exact way to send the callback to my activity behavior from my Listener class.

It will be a great help if any one help me in this. Thanks in advance