Plaid Cymru leader Adam Price is self-isolating after his son showed one of the coronavirus symptoms.
It comes as Prime Minister Boris Johnson said "drastic action" now needs to be taken as he outlined new measures to try and combat coronavirus.
The Plaid Cymru leader said he "will continue to work from home."
Two other assembly member have also gone into self-isolation over coronavirus fears.
Mark Reckless, Brexit Party group leader and Neil McEvoy, the independent AM for South Wales Central said they will self isolating for 14 days.
People across the UK have been told to avoid pubs, clubs and theatres, stop all non-essential contact and travel, and work from home if they can.
As part of the measures, anyone living in a household with somebody who has either a persistent cough or fever must now also isolate themselves for 14 days.
By the weekend, those groups particularly vulnerable to coronavirus will be asked to stay at home for 12 weeks.
What does the government mean by 'social distancing?'
- Avoid contact with someone who is unwell.
- Avoid public transport.
- Work from home.
- Avoid large gatherings.
- Avoid gathering with friends and family.