It could be that you have an independent chair at your viva; they would be a member of staff from your university. Their role in the viva would be, largely, to observe what happens.
There are lots of reasons you might have an independent chair:
- Their presence could be part of the regulations for your university.
- It may be part of the culture for your department to have one.
- One of your examiners might be a fairly new academic and so it’s been thought to be good to have an experienced member of staff present.
- It may even be that your viva has been randomly selected to be observed, so that your institution can be confident that vivas are being held in an appropriate way!
There are lots of reasons you might have one, but no bad ones: an independent chair is there to watch and to make sure that the viva is going well. They won’t have read your thesis. They won’t ask you any questions. They will make sure the process is fair.
An extra person in the room might add to nerves, but really the best thing you can do is check far in advance what the situation will be or might be for your viva. Then you can do anything you need to do in order to be comfortable on the day.