From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
Mousey is a small Mouse.
 Dragon Ball
Mousey scurried into the middle of the fight between General Blue and Son Goku in the Pirate Cave. He startled Blue and made his Telekinesis on Goku wear out, thus giving Goku the upper hand again. When Kuririn and Bulma Brief went ahead of Goku while he got the Dragon Ball, Goku stopped to save Mousey and ran off with him in his mouth. They reached the surface again and ended up at General Blue's Camp where Goke then let Mousey go.
- Mousey is the name Goku gave him.