If confirmed, they would be Germany's first cases of the virus but Schroeder sought to calm fears of a swine flu pandemic in the country.
These are "single isolated cases from abroad and we do not have a spreading disease here in our own country," Schroeder said.
Germany is "well prepared" for an outbreak of swine flu, the state secretary added.
A married couple recently returned from holiday in Mexico is under observation in southern Germany, said Joerg Hacker, the head of the Robert Koch Institute, which is responsible for disease control and prevention.
The woman is suffering mild symptoms of the disease, Hacker said, adding that the results of tests should be available late Tuesday or early Wednesday. A third case is also being examined, he added.
Two of the three patients have begun to recover, Hacker said.
On Monday, Germany's foreign ministry advised citizens against all non-essential travel to Mexico, where the probable death toll from the virus has risen to 152.
Germany's leading tourism group, TUI, said it would cancel Mexico City visits until May 5 owing to the swine flu outbreak and would offer alternatives to clients who had planned to travel to other parts of Mexico.