Chandrasiri Bandara, who writes an astrology column for a pro-opposition weekly, was taken in on Thursday, police spokesman Ranjith Gunasekara said.
"The CID (Criminal Investigations Department) is questioning the astrologer," Gunasekara said Friday, adding that they wanted to find out the "basis" for the prediction.
The astrologer had predicted that a planetary change on October 8 will be inauspicious for parliament and the government may not be able to arrest rising living costs -- a prediction already made by private economists.
The opposition United National Party condemned Bandara's arrest and accused the government of heading towards a dictatorship.
"The crime which Chandrasiri Bandara committed was publishing an astrological column which was adverse to the government," UNP general secretary, Tissa Attanayake, said.
Sri Lankan politicians take astrology seriously and most have their own personal seers who decide the auspicious times to launch any new programme or work.