Much of the attention had been on whether Lionel Messi would add to his record 50 league goals this term but the World Player of the Year had a quiet game and was upstaged by Betis striker Ruben Castro.
Sergio Busquets headed Barca in front from a corner after nine minutes. A second yellow card for defender Dani Alves in the 53rd then turned the game on its head and opened the way for a Betis fight-back.
Castro burst clear to lob keeper Victor Valdes in the 71st minute and he also broke through the middle to add his second goal three minutes later.
Messi struck the post with a free kick just before Keita flung himself at a cross to level matters.
Second-placed Barca finished with 91 points from 38 matches, six short of champions Real Madrid who can beat their La Liga points record of 99 with a win at home to Real Mallorca on Sunday.
Barca still have the King's Cup final to play against Athletic Bilbao on May 25 before Guardiola hands over the reins to his assistant Tito Vilanova.
The Catalans will be chasing their 14th trophy from the coach's four years in charge.
"I don't think the league will miss me. The league was here before, and will continue after me," a downbeat Guardiola said following the draw.
"After Dani's sending off it was a different game. We lost control because playing with 10 is always more difficult.
"In the end it was a good goal from Seydou. He is a player who probably deserves to play more."
Elsewhere in Spain, Valencia , 30 points behind Barca in third spot, said farewell to coach Unai Emery after a 1-0 defeat at Real Sociedad .
French winger Antoine Griezmann scored the only goal after 64 minutes.
Argentine Mauricio Pellegrino will take over from Emery who is reported by local media to be close to joining Spartak Moscow.
Emery, a manic touchline presence, leaves Valencia after guiding them to automatic qualification to the Champions League for the third year in a row.