Mucha, who is a senior aide to Polish President Andrzej Duda, said in a social media post on Thursday that he tested positive for COVID-19 while quarantining.
He added that he was remaining in isolation.
“While staying in quarantine, I took a COVID-19 test, and I tested positive," Mucha said in a tweet. "I am isolating myself."
He appealed to Poles to take care of themselves and their loved ones, including seniors.
"A lot depends on us. The disease strikes at random, but we can limit its spread. Social distancing, disinfecting, mask wearing," Mucha said.
His message came after the Polish head of state told private broadcaster Polsat a day earlier that he was in good health after testing positive for the coronavirus at the end of last week and developing some mild symptoms since then.
Meanwhile, the Polish president's press spokesman Błażej Spychalski said in a social media post on Monday that he was experiencing COVID-19 symptoms while in quarantine.
Poland on Thursday reported a record 20,156 new coronavirus infections and a record 301 new deaths, its worst daily toll since the start of the pandemic.
A total of 319,205 people have tested positive for the coronavirus in the country since the pandemic began, and 5,149 have died in connection with the COVID-19 respiratory disease so far, public health officials announced.