Those who are a sleep in Jesus are those believers that have already died.
Bema seat is the judgement that believers will receive concerning what they have done for Christ.
1 Cor 3:
10According to the grace of God given to me, like a skilled master builder I laid a foundation, and someone else is building upon it. Let each one take care how he builds upon it.
11For no one can lay a foundation other than that which is laid, which is Jesus Christ.
12Now if anyone builds on the foundation with gold, silver, precious stones, wood, hay, straw—
13each one’s work will become manifest, for the Day will disclose it, because it will be revealed by fire, and the fire will test what sort of work each one has done.
14If the work that anyone has built on the foundation survives, he will receive a reward.
15If anyone’s work is burned up, he will suffer loss, though he himself will be saved, but only as through fire.
More of the Bema seat here.