Hi Mingho,
The sap.ui.model.Model class exposes the requestSent, requestCompleted, requestFailed and parseError events. You can try to work out some logic, like perhaps, show the progress indicator when requestSent is fired, and hide the progress indicator when requestCompleted/requestFailed/parseError is fired. Better yet, show the BusyIndicator as Christian Jianelli suggested above using these events to start/stop it.
You can attach to these events using the methods attachRequestSent, attachRequestCompleted etc. on your OData model.
More information here (Control reference -> Model -> attachRequestSent())
Hope this helps.
Regards,
Pritin