At the moment these events have not been processed into the ePO DB. You can delete these events if you wish, but of course this means that they will be gone forever. As long as that's OK with you, go ahead.
It might be worth checking the eventparser log to see if there are problems processing events - if there are then the problem may reoccur.
You can delete these events with event parser service stopping, only thing is you will not able to view client and Thret event logs on those machines. This issue occur when huge multiple events came to ePO console and ePO was unable to dump those into DB. Try to analyze incoming events and try to reduce unwanted events by removing report option in AP or Event Filtering in ePO settings, this will improve ePO functionality.