Try this query
SELECT *
FROM (
SELECT *, @rowNo := if(@pv = week, @rowNo+1, 1) as rNo, @pv := week
FROM (
SELECT keyword_id, COUNT(*), YEARWEEK(FROM_UNIXTIME(created)) AS week
FROM keyword_sentence
WHERE
FROM_UNIXTIME(created) >= CURRENT_DATE - INTERVAL 2 MONTH
AND
FROM_UNIXTIME(created) < CURRENT_DATE - INTERVAL 1 MONTH
GROUP BY week, keyword_id
ORDER BY week, COUNT(*) DESC
) temp
JOIN (
SELECT @rowNo := 0, @pv := 0
) tempValue
) tmp
WHERE
tmp.rNo < 6
Fiddle
Hope this helps