The colleagues all work at the depot off Delta Way.
Arriva say they are supporting any colleagues who have been asked to self-isolate by NHS Test and Trace.
A spokesman for Arriva would not confirm how many other colleagues have been asked to self-isolate.
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Simon Mathieson, area managing director for Arriva said “The safety of our customers and colleagues is Arriva’s number one priority. We are being guided every step of the way by expert organisations such as the Health and Safety Executive and Public Health England.
"We can confirm that three colleagues have tested positive for Covid-19 and in line with NHS Test and Trace we are fully supporting any colleagues who may be requested to self-isolate by NHS Test and Trace or a public health professional.
"We will continue to follow all the latest guidance to keep our workspaces and buses Covid-19 secure and our colleagues and customers safe."