TV cameras caught Koepka staring at an official and pointing to his wrist when Holmes was playing. CBS analyst Peter Kostis made a similar complaint about Holmes' pace of play during February's Genesis Open.
"It was slow, but it wasn't that bad for his usual pace," Koepka told reporters Sunday. "I thought it was relatively quick for what he does."
Koepka acknowledged he wished Holmes played faster, but added pace of play is a problem throughout golf.
"He doesn't do anything until it's his turn," Koepka said. "That's the frustrating part. But he's not the only one that does it out here."
Koepka finished the British Open tied with Lee Westwood for fourth place at 6-under for the tournament. He shot a 3-over 74.
Koepka won the 2019 PGA Championship and finished second at this year's Masters.
Holmes tied for 67th at 5-over and shot 16-over 87 Sunday. He didn't speak to reporters.
"He had a rough day, but J.B. is a slow player," Koepka said. "I know it's difficult with the wind, but I didn't think he was that bad today."