The suspects include three English-speaking men and a Burmese maid and her husband, according to Bangkok's police chief Sanit Mahathavorn.
Police said they are still confirming the nationalities of the three English speakers, who were reported in local media to be two Americans and one Briton.
One of the suspects grabbed a gun and opened fire on police during the raid, injuring an officer, police told reporters.
Police then discovered a dead body, carved up into pieces, inside a large freezer on the ground floor.
Officers initially told media it was a woman but later determined it was a "foreign man with blond hair," said Sanit.
"His body was cut with sharp object into six pieces, put in a black bag and brought into the freezer," the police chief told reporters, adding that the suspects have been brought to a station in southwest Bangkok for further interrogation.
Police said they also found forged passports, three guns and crystal meth inside the building, which the group had rented for three months.
"Tourism police investigated and found out that international criminals were staying at that place and using it to do wrong things," Thailand's tourist police commander, Surachet Hakpan, told reporters after the raid.