In their last 11 games, Barca have kept eight clean sheets and Keita believes they need to do likewise against a Chelsea team he admits are a "great side".
"It's very important to win and not to let a goal in," said Keita.
Barca are in the midst of a hectic end to the season as they chase honours on three fronts.
Not only are they in the Champions League semi-finals, but they are four points clear at the top of the Primera Division summit with five games remaining and also in final of the Copa del Rey.
That means the Catalan giants have little respite between matches, but nevertheless Keita insists coach Pep Guardiola's preparations are still meticulous and they will know everything they need to know about Chelsea by the time they face Guus Hiddink's men.
"The coach does a great job in preparing for matches. We see a lot of their games and we analyse their weak points and the dangers they could pose to us," he said.
"They (Chelsea) are an opponent we know well, they are a great side. We've seen how they play in both the Premier League and the Champions League.
"They are a difficult team, with physically very strong players, and a team who are capable of causing you problems at any time."
Barca's bid to win their first Primera Division title since 2006 suffered a setback on Saturday when they were held to a 2-2 draw by Valencia, ending a run of seven successive league wins for Guardiola's side.
However, Barca are still in a strong position above arch rivals Madrid, and Keita insists the players remain in confident mood.
"The team is very calm because we are working well. We are only thinking of ourselves, it's not necessary to look at what Madrid are doing. If we do things well then in the end we will not have to suffer," he added.
Tuesday's clash with Chelsea is not the only huge match Barca have this week.
On Saturday they must travel to the Bernabeu where they face second-placed Madrid in a match that could go a long way to deciding the Primera Division title.
Barca midfielder Xavi said on Catalunya Radio: "If we win at the Bernabeu, the league would be decided.
"We have the hope and the desire to win there, and sign off an excellent campaign for the team.
"We've worked hard to get where we are, we now have a key week for the Champions League and league."