The Plymouth Argyle striker, 26, had been at The Den since the end of September, scoring once in six appearances for the promotion-chasing Lions.
Easter will remain with Colchester until the end of the year, after agreeing to cancel his loan deal at Millwall.
The forward has found the net only six times in his 12 months with the Pilgrims, in sharp contrast to his prolific time with Wycombe where he scored 28 goals in 54 starts for the Chairboys.