The bomb was planted beside the outer wall of the mosque in Landi Kotal town in the Khyber tribal region, local administration chief Shakeel Burki said.
"The blast killed a four-year-old girl and wounded three others, one of them seriously," he said.
No one has claimed responsibility of the blast which came a day after a bomb placed in a mosque in a densely populated neighbourhood of Peshawar went off during afternoon prayers, killing six people.
Peshawar is vulnerable to bomb blasts and Taliban attacks as it runs into the semi-autonomous tribal belt, considered a safe haven for Taliban, al Qaeda and other insurgents fighting both in Pakistan and across the border in Afghanistan.
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