Taking care of the mosques and tidying the furniture etc inside them is something that is praiseworthy and encouraged. The one who does that will be rewarded Allaah for this good deed. 
Allaah has commanded us to venerate the mosques as He says (interpretation of the meaning): 
“In houses (mosques) which Allaah has ordered to be raised (to be cleaned, and to be honoured), in them His Name is remembered [i.e. Adhaan, Iqaamah, Salaah (prayers), invocations, recitation of the Qur’aan]. Therein glorify Him (Allaah) in the mornings and in the afternoons or the evenings

Suratul-Noor 24:36