anxious / eager
Uneasy waiting versus happy readiness.
Use anxious when worry or unease is part of the feeling: anxious about the results. Use eager when the feeling is only keen desire: eager to start. Anxious to please is established when the desire carries strain. If the mood is bright, eager is the word.
Examples
UseShe was anxious about the biopsy.
UseThe children were eager to open the box.
AvoidThe children were anxious to open the box. (If no worry is meant.)