This study investigates infants' neural and behavioral responses to maternal ostensive signals during naturalistic mother-infant interactions and their effects on object encoding. Mothers familiarized their 9- to 10-month-olds (N = 35, 17 females, mainly White, data collection: 2018-2019) with objects with or without mutual gaze, infant-directed speech, and calling the infant's name. Ostensive signals focused infants' attention on objects and their mothers. Infant theta activity synchronized and alpha activity desynchronized during interactions compared to a nonsocial resting phase (Cohen' d: 0.49-0.75). Yet, their amplitudes were unrelated to maternal ostensive signals. Ostensive signals did not facilitate object encoding. However, higher infant theta power during encoding predicted better subsequent object recognition. Results strengthen the role of theta-band power for early learning processes.