Rau was speaking after Biden won the state-by-state Electoral College vote that officially determines the US presidency.
Asked about what could be expected of Biden's term in office, Rau predicted that American foreign policy would continue as under outgoing President Donald Trump.
"This is due to the simple fact that the foreign interests of the United States, regardless of who resides in the White House, are constant, and nothing changes here," the Polish foreign minister added.
Rau said he was confident the US would continue to maintain troops in Poland, adding that from the American perspective "nobody and nothing" would be able to replace Poland on NATO's eastern flank.
Polish Defence Minister Mariusz Błaszczak said last month that both Republican and Democratic politicians in the United States see “the importance of Poland’s strategic partnership” with their country.
His comments came after a new US Army headquarters began operating in Poland following its official launch in the western city of Poznań.
Meanwhile, Poland's president on November 9 ratified a major military deal with the United States under which at least 1,000 extra American troops can be stationed in his country.
The deal had long been sought by Poland, a staunch US military ally fearful of Russia. Around 4,500 American troops are already stationed in Poland on a rotating basis.