Highlighting is an option for CHM output (Microsoft HTML help) but not for WebHelp in this version. Later versions of RoboHelp offer search highlighting in output. Or, you may find that ZoomSearch will as well.
Click here for fellow Adobe Community Professional Peter Grainge's site where ZoomSearch is described
Helpful and Handy Links
OK, thank you for your prompt reply!
See www.grainge.org for RoboHelp and Authoring tips