Yes Barcelona was 12th out of 14 teams on 1941-42 La Liga, as seen in the article in Wikipedia.
Oviedo was 11th, Barcelona 12th, Alicante 13th and Real Sociedad 14th. Those years, the two last teams in the classification were relegated to Segunda División. The two teams above them, that is on 11th and 12th position, played a relegation play-off versus some teams from Segunda División.
From what I see, Segunda División on 1941-42 consisted on three groups. The two best teams of each group would join in a little league on a round-robin method. The two first teams on that league would be promoted to Primera División, while the next two would play versus the 11th and 12th from Primera División: 3rd vs 12th and 4th vs 11th.
In that specific year, Real Betis and Zaragoza FC were promoted to Primera División, Real Murcia CF was 3rd in that league and CD Sabadell CF was 4th. Thus, Barcelona played vs Real Murcia on 28th June 1942 and the result was 5-1 for Barcelona, so they remained in the Primera División.
Both matches Barcelona vs Murcia and Oviedo vs Sabadell were played in Madrid, as a neutral stadium, and you can see the report of the match in the periodicals library of Mundo Deportivo:
The headline says:
The champions of Spain remain in Primera División.