The economics Nobel is not one of Alfred Nobel's own prizes but a Riksbank prize in his memory
Background
The Nobel Prize announcements are made in October each year, and the prize in economic sciences stands apart from the rest. The Nobel Prize organisation's own pages record that in 1968 Sveriges Riksbank, Sweden's central bank, established the Sveriges Riksbank Prize in Economic Sciences in Memory of Alfred Nobel. The prize is based on a donation received by the Nobel Foundation in 1968 from Sveriges Riksbank on the occasion of the bank's 300th anniversary. The prize amount is the same as for the Nobel Prizes and is paid by the Riksbank. The first prize in economic sciences was awarded to Ragnar Frisch and Jan Tinbergen in 1969. The prize is awarded by the Royal Swedish Academy of Sciences, Stockholm, according to the same principles as for the Nobel Prizes that have been awarded since 1901.
In plain words
Sveriges Riksbank Sveriges Riksbank — Sweden's central bank, which funded and gave its name to the prize in economic sciences.