Junaid Jamshed, who quit music to join a deeply conservative Sunni Muslim group, made his remarks in a video.
Another Sunni Muslim group accuses him of blasphemy. He has since apologised.
Blasphemy allegations are hugely sensitive in Pakistan. Those convicted face a potential death sentence.
The laws on blasphemy are often used to settle scores or target members of Pakistan's minorities.
But the BBC's Shaima Khalil in Islamabad says what makes Junaid Jamshed's case so unusual is the fact that he is a high-profile, wealthy Muslim preacher.
In his video broadcast, which has since been widely shared, he appeared to make negative remarks about the Prophet's youngest wife Ayesha.
He described how Ayesha demanded attention from the Prophet and how one day she faked an illness.
The video led to another Muslim group, Sunni Tehrik, filing the blasphemy case.
Junaid Jamshed - who is called "Disco Mullah" because of his role with the Tablighi Jamaat organisation - released a further video after the incident pleading for forgiveness.
"I confess to my mistake. I did not do it intentionally," he said.
"With a clean heart I ask that Allah forgive me and I beg and beseech all Muslims to forgive me. This was not on purpose."
But the complainant, Sunni Tehrik spokesman Mohammad Mobeen Qadri, told BBC Urdu that an apology could not stop the legal process once blasphemy had been committed.
Before embarking on his religious career, Jamshed was a member of Vital Signs, a number of whose songs and albums topped the charts.
He is currently incommunicado and his whereabouts are unclear, the BBC's M Ilyas Khan in Islamabad reports.
"Now the case is with the investigators," Mehmood Ahmed, a police officer in Karachi, told Reuters news agency.
"We will have to arrest Junaid Jamshed and it is up to him if he moves bail and goes to court against this."
From pop star to preacher
Additional reporting by M Ilyas Khan
Police in Pakistan are investigating a former pop star-turned-Muslim campaigner for blasphemy after he was caught on camera allegedly insulting one of the Prophet Muhammad's wives.