Koeman was shown a red card for comments he supposedly made to the fourth official not long after Granada had drawn level at Camp Nou on Thursday.
The Dutchman then watched on from the stands as the home side conceded again in the 79th minute, substitute Jorge Molina heading home to provide a further twist in the title race.
"I don't understand why they have sent me off. They [said I] have disrespected the fourth official," Koeman said after Thursday's match, according to Marca.
"I don't understand the red. According to the delegate, it was a lack of respect for the fourth official. I haven't said anything. I haven't insulted him or anything. But hey, if the fourth official wants to be the star of the night ... thank you."
Barcelona had appeared set to take over at the top of the table but now sit two points behind LaLiga leaders Atletico Madrid with five games remaining.
One of those matches sees Barca host Atleti on May 8, which will be covered by Koeman's suspension unless his appeal is successful. The other fixture will be Sunday's trip to Valencia.
In confirming the appeal, the club referenced that their head coach had not previously been sent off since taking charge.
Meanwhile, Barca have extended Oscar Mingueza's contract.
The defender, who made his first-team debut in a Champions League fixture against Dynamo Kiev in November, is now tied down until June 2023 with a release clause of €100million.
"It's a dream come true. I've been working for many years for this objective, to sign a contract with the first team," Mingueza said in an official club interview.
"I'm really happy, really proud to have this chance after all the support that I have received."
Mingueza has made 36 appearances in all competitions this season since his promotion from the B team.