I bought Ketorin 25mg (Ketoprofen) in Helsinki, Finland, and I wonder
if it is the same as one of the over-the- counter pain relievers in
the USA? If so, which one?

Ketoprofen is indeed available over the counter in the US. Brand names
include "Orudis," "Oruvail," and "Actron." It can also be bought
generically, as ketoprofen.

"Orudis and Actron are over-the-counter versions of the prescription
drug ketoprofen. They provide temporary relief from headache,
toothache, muscle ache, backache, arthritis, menstrual cramps, and the
minor aches and pains of a cold. They also reduce fever."

PDR Health
http://www.pdrhealth.com/drug_info/otcdrugprofiles/drugs/fgotc173.shtml

More info is available here:

RxList: ketoprofen
http://rxlist.com/cgi/rxlist.cgi?drug=ketoprofen

I hope this is precisely the information you need. If anything is
unclear or incomplete, please request clarification; I'll gladly offer
further assistance before you rate my answer.

Best regards,
pinkfreud