Reykjavík Airport is the city airport in Reykjavík and is primarily used for domestic travel. It is convenient for reaching other Icelandic regions from a stay in the capital, but it is separate from Keflavík International Airport on the Reykjanes peninsula.
Confirm the terminal used by your airline and arrange the local transfer by taxi or public transport as appropriate. A connection from an international arrival at Keflavík requires a separate road journey between airports. Leave enough time for that transfer, check-in and any delay rather than treating the two airports as one terminal complex.