、。
This year again, regular concerts by amateur musicians are being frequently held.
Literal
This-year [also-も], amateur musician [genitive-の] regular concerts [subject-が] frequently are-being-held.
An event-news sentence. 定期演奏会 ('regular/periodic concert') is a stock term in music-club and orchestra contexts — 定期 (regular, periodic) + 演奏会 (concert). 開催される is the passive of 開催する ('hold/conduct an event') — the passive is the normal voice for events being held. The pattern 今年も ('this year too') implies there was a similar situation last year, making this a recurring annual event. 頻繁に ('frequently') is an adverbial form of 頻繁 ('frequent').