West Tyrone representative Daniel McCrossan has closed his office to the public as a precaution.
He received a positive test result on Friday, after testing negative for the virus earlier in the week.
“Early on Monday I was made aware that I had been in contact with someone who was demonstrating symptoms of Covid-19. I immediately booked a test and informed my colleagues that I would not be able to attend plenary sessions in the Assembly this week as a result,” he said.
“Late on Tuesday I received a negative test result. This was a huge relief, but unfortunately at that time a member of my household received a positive test result and, in line with the public health guidelines, I have remained in isolation at home.
“Late on Wednesday I began experiencing symptoms of the virus – headache, fever and a new cough. I booked another test for Thursday and received the positive result today.”
Mr McCrossan said his priority is to keep those around him safe.
“This has been a distressing time but my first priority is to keep those around me safe,” he said.
“I immediately reported the result on the Stop Covid app and have taken the decision to close my Assembly office to the public as a precaution against transmission of the virus and to ensure the safety of local people.
“This virus spreads so easily, the member of my household and others who were tested had no symptoms at first. It’s a frightening reality.
“This virus is still very much with us and I would urge everyone to please follow the public health guidelines, to maintain social distancing, continuing washing hands and to get tested if you show any symptoms at all.
“This is the only way we can keep infection rates low and protect the vulnerable and elderly.”
Mr McCrossan said he will continue to work in isolation.
On Friday the Department of Health announced two further deaths with Covid-19 in Northern Ireland, bringing the total toll in the region to 575.
A further 163 new confirmed cases of Covid-19 were reported in the last 24-hour reporting period, bringing the total number of cases in the region to 8,943, including 763 in the last seven days.