Three policemen, who have returned from West Bengal after poll duty, were among the newly-infected people, the official said.
The policemen initially tested negative upon their arrival on April 27.
Besides, 13 Border Security Force (BSF) jawans, who have travel history, 3 frontline workers and 12 children have tested positive for Covid19, he said.
He said at least 2,937 samples were tested in the last 24 hours and 4.76% of them came out positive for Covid19.
Of the 140 new cases, Aizawl district reported the highest cases at 100, followed by Serchhip district, which reported 18 cases, he said.
A total of 12 cases were reported from Kolasib district, 7 cases from Lawngtlai district and 3 cases were reported from Lunglei district.
A total of 71 patients have travel history while the rest 69 were found to have locally infected, the official said.
Of the 69 locally-infected patients, 40 have direct contact with positive patients and it is to ascertain how 29 patients were infected by the virus.
A total of 43 patients have developed symptoms of Covid19 and the rest are asymptomatic.
So far a total of 6,019 people have tested positive for Covid19 in Mizoram.
The number of active Covid19 cases in Mizoram now stands at 1,122 while 4,882 people have recovered from the disease.
The recovery rate of Mizoram is 81.11%.
The Covid19 death toll in the state reached 15 on Friday as two more men aged 82 and 47 have succumbed to the infection.
The 82-year-old victim was diagnosed with Covid19 on Wednesday, officials said.
He died at Zoram Medical College (ZMC) around 5.45 am on Friday, they said.
The other victim was diagnosed with Covid19 on April 23 and was shifted from a Covid19 Care Centre (CCC) to ZMC the next day for treatment.
The patient succumbed to the infection around 9.20 am on Friday, according to officials.
Mizoram has so far conducted test of 3,03,859 samples out of which 1.98% have tested positive for Covid19.
Meanwhile, state immunisation officer Dr. Lalzawmi said 2,01,043 people, including 50,910 senior citizens, have been administered the first dose of Covid19 vaccine till Thursday and 45,435 of them have received both doses of the vaccine.